Agent Platform Error Logs for Flow Runs

[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?

Closes #1500
Logs possible platform errors that may arise when deploying a flow run

e.g. using the Fargate agent with the name of a cluster that does not exist at time of deploy:

Why is this PR important?

Makes some logs easier to see without having to go to the agent itself

[codecov]

Codecov Report

Merging #1528 into master will increase coverage by 0.03%.
The diff coverage is 100%.

[cicdw]

Awesome! This will be super helpful - and thanks for the solid tests, too 🚀