Compressing the discovery cache

[jorenham]

#2315 shaved off a bit more than 20MB of the discovery cache, by removing the json indentation.
Currently there's still 74.6MB remaining, and it appears to be growing steadily over time (from 81MB on 2023-03-31 to 94MB on 2024-01-15).

So while #2315 definitely helped, I believe that it's a good idea to consider reducing the size even further. I believe that this could significantly improve build/deploy times of the many docker images that use this library. For reference, the current latest python-slim docker image is less than 50MB.

An easy win would be to use compression.
To illustrate: if I manually zip the entire documents directory of 74.6MB in v2.114.0 using the pop-os default gnome archive manager, I end up with an archive of 11.9MB.
Creating a documents.tar.xz in the same way makes this 4.6MB.

It should be possible to achieve similar levels of compression by using Python's standard compression libraries, e.g. zlib, zipfile, or lzma.

[parthea]

PRs are welcome!

We should ensure that when we retrieve the discovery artifact from the compressed file using get_static_doc that we only extract the file for the requested service and version.

google-api-python-client/googleapiclient/discovery_cache/__init__.py

Lines 55 to 78 in c965b05

	def get_static_doc(serviceName, version):
	"""Retrieves the discovery document from the directory defined in
	DISCOVERY_DOC_DIR corresponding to the serviceName and version provided.
	Args:
	serviceName: string, name of the service.
	version: string, the version of the service.
	Returns:
	A string containing the contents of the JSON discovery document,
	otherwise None if the JSON discovery document was not found.
	"""
	content = None
	doc_name = "{}.{}.json".format(serviceName, version)
	try:
	with open(os.path.join(DISCOVERY_DOC_DIR, doc_name), "r") as f:
	content = f.read()
	except FileNotFoundError:
	# File does not exist. Nothing to do here.
	pass
	return content