camelCase -> snake_case

[cicdw]

Thanks for contributing to Prefect!

Please describe your work and make sure your PR:

• adds new tests (if appropriate)
• updates CHANGELOG.md (if appropriate)
• updates docstrings for any new functions or function arguments, including docs/outline.toml for API reference docs (if appropriate)

Note that your PR will not be reviewed unless all three boxes are checked.

What does this PR change?

This PR does some major house cleaning to:

• remove Client.deploy and flow.deploy
• remove Client.write_run_log
• converts most (but not all) all of our camelCased GraphQL calls to snake_cased calls

Note that we should manually test many of the changes here to make sure a breaking change doesn't sneak in accidentally.

Why is this PR important?

• Closes Remove flow.deploy and client.deploy #2183
• Closes Remove client.write_run_log #2184
• Closes Convert all GraphQL calls to snake case #2181

[codecov]

Codecov Report

Merging #2185 into master will increase coverage by 0.05%.
The diff coverage is 81.39%.