Address Sphinx Warnings in Docs Warnings Presubmit

[ohmayr]

Once we disable the setting to treat warnings as errors as part of the performance initiative, we need to investigate which warnings need to be addressed and whether they need a fix upstream. We will also be getting rid of https://github.com/googleapis/google-cloud-python/blob/main/.librarian/generator-input/client-post-processing/doc-formatting.yaml . If we find that any of these replacements are actually making docs more readable, we should make sure to surface them and make a plan to address it