docs: adds guide for oauth2 strategy with google (#484) #1043

Job	Run time
mix deps.get	30s
mix hex.audit	29s
MIX_ENV=test mix.compile	50s
mix credo --strict	44s
mix git_ops.check_message	40s
mix doctor --full --raise	36s
mix dialyzer	7m 2s
mix format --check-formatted	49s
mix ash_postgres.generate_migrations --check	48s
mix sobelow --config	36s
mix spark.cheat_sheets --check	34s
mix spark.formatter --check	36s
mix test	1m 13s
mix deps.unlock --check-unused	34s
MIX_ENV=dev mix.compile	42s
mix docs	59s
mix git-ops.release	41s
Deploy docs to GitHub pages.	10s
	18m 33s

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