Add custom www-gitlab-com image with patched gsutil rsync command

Currently the `gsutil rsync` command does not support the `-z` or `-Z`
options available in `gsutil cp` to compress files locally via gzip
before uploading
(https://github.com/GoogleCloudPlatform/gsutil/issues/579). As
https://cloud.google.com/storage/docs/gsutil/commands/cp states:

When you specify the -z option, the data from your files is
compressed before it is uploaded, but your actual files are left
uncompressed on the local disk. The uploaded objects retain the
Content-Type and name of the original files, but have their
Content-Encoding metadata set to gzip to indicate that the object data
stored are compressed on the Cloud Storage servers and have their
Cache-Control metadata set to no-transform.

about.gitlab.com is currently serving uncompressed HTML files because
`Cache-Control: max-age=0` is set (see
https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/87045),
and Fastly has a custom rule to skip HTML files and therefore won't
cache them.

This patches the `rsync.py` using
https://github.com/GoogleCloudPlatform/gsutil/pull/1430 to support these
command-line options so local gzip compression can be performed.

Relates to
https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/14852

patches/gsutil/rsync_gzip.patch

@@ -0,0 +1,100 @@
+diff --git a/gslib/commands/rsync.py b/gslib/commands/rsync.py
+index 734a8dbf0..0897d74a5 100644
+--- a/gslib/commands/rsync.py
++++ b/gslib/commands/rsync.py
+@@ -527,6 +527,58 @@
+                  use ^ as an escape character instead of \\ and escape the |
+                  character. When using Windows PowerShell, use ' instead of "
+                  and surround the | character with ".
++
++  -z <ext,...>   Applies gzip content-encoding to any file upload whose
++                 extension matches the ``-z`` extension list. This is useful when
++                 uploading files with compressible content such as .js, .css,
++                 or .html files, because it reduces network bandwidth and storage
++                 sizes. This can both improve performance and reduce costs.
++
++                 When you specify the ``-z`` option, the data from your files is
++                 compressed before it is uploaded, but your actual files are
++                 left uncompressed on the local disk. The uploaded objects
++                 retain the ``Content-Type`` and name of the original files, but
++                 have their ``Content-Encoding`` metadata set to ``gzip`` to
++                 indicate that the object data stored are compressed on the
++                 Cloud Storage servers and have their ``Cache-Control`` metadata
++                 set to ``no-transform``.
++
++                 For example, suppose the directory ``cattypes`` contains the
++                 following files:
++
++                 - ``cattypes.html``
++                 - ``tabby.jpeg`
++
++                 The following command:
++
++                   gsutil rsync -z html cattypes/ gs://mycats
++
++                 does the following:
++
++                 - The ``rsync`` command uploads the directory `cattypes`
++                   to the bucket ``gs://mycats``.
++                 - Based on the file extensions, gsutil sets the ``Content-Type``
++                   of ``cattypes.html`` to ``text/html`` and ``tabby.jpeg`` to
++                   ``image/jpeg``.
++                 - The ``-z`` option compresses the data in the file ``cattypes.html``.
++                 - The ``-z`` option also sets the ``Content-Encoding`` for
++                   ``cattypes.html`` to ``gzip`` and the ``Cache-Control`` for
++                   ``cattypes.html`` to ``no-transform``.
++
++                 Because the ``-z/-Z`` options compress data prior to upload, they
++                 are not subject to the same compression buffer bottleneck that
++                 can affect the ``-j/-J`` options.
++
++                 Note that if you download an object with ``Content-Encoding:gzip``,
++                 gsutil decompresses the content before writing the local file.
++
++  -Z             Applies gzip content-encoding to file uploads. This option
++                 works like the ``-z`` option described above, but it applies to
++                 all uploaded files, regardless of extension.
++
++                 CAUTION: If some of the source files don't compress well, such
++                 as binary data, using this option may result in files taking up
++                 more space in the cloud than they would if left uncompressed.
+ """)
+ # pylint: enable=anomalous-backslash-in-string
+ 
+@@ -1580,7 +1632,7 @@ class RsyncCommand(Command):
+       usage_synopsis=_SYNOPSIS,
+       min_args=2,
+       max_args=2,
+-      supported_sub_args='a:cCdenpPriRuUx:j:J',
++      supported_sub_args='a:cCdenpPriRuUxz:Zj:J',
+       file_url_ok=True,
+       provider_url_ok=False,
+       urls_start_arg=0,
+@@ -1732,6 +1784,7 @@ def _ParseOpts(self):
+     # The gzip_encoded flag marks if the files should be compressed during
+     # the upload.
+     gzip_encoded = False
++    gzip_local = False
+     gzip_arg_exts = None
+     gzip_arg_all = None
+     if self.sub_opts:
+@@ -1779,10 +1832,19 @@ def _ParseOpts(self):
+             self.exclude_pattern = re.compile(a)
+           except re.error:
+             raise CommandException('Invalid exclude filter (%s)' % a)
++        elif o == '-z':
++          gzip_local = True
++          gzip_arg_exts = [x.strip() for x in a.split(',')]
++        elif o == '-Z':
++          gzip_local = True
++          gzip_arg_all = GZIP_ALL_FILES
+ 
+     if self.preserve_acl and canned_acl:
+       raise CommandException(
+           'Specifying both the -p and -a options together is invalid.')
++    if gzip_encoded and gzip_local:
++      raise CommandException(
++          'Specifying both the -j/-J and -z/-Z options together is invalid.')
+     if gzip_arg_exts and gzip_arg_all:
+       raise CommandException(
+           'Specifying both the -j and -J options together is invalid.')