Add default 30s timeout to client requests

[joshmeek]

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?

Updates the Client requests to have a default timeout of 30 seconds

Why is this PR important?

Without providing a timeout it has the potential to hang indefinitely

[codecov]

Codecov Report

Merging #1672 into master will decrease coverage by 0.01%.
The diff coverage is 66.66%.