docs: Added documentation on log_level and excluded_loggers params in setup_logging

[gkevinzheng]

Googlers, please look at b/234303349 for more context.

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• docs/std-lib-integration.rst:24, tag logging_setup_logging
• docs/std-lib-integration.rst:29, tag logging_setup_logging_excludes
• samples/snippets/usage_guide.py:478, tag logging_setup_logging
• samples/snippets/usage_guide.py:482, tag logging_setup_logging_excludes

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• samples/snippets/usage_guide.py:478, tag setup_logging
• samples/snippets/usage_guide.py:482, tag setup_logging_excludes

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