Kubernetes Job Environment

[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?

Adds a KubernetesJobEnvironment which is very similar to how the DaskKubernetesEnvironment operates but it only deploys based on a single job spec.

Why is this PR important?

There are a myriad of possible k8s configuration options for deployments so we should expose an environment which allows for users to easily provide a job spec. This helps address (and will be documented in the future) priorities, eviction policies, resource requests, sidecars, etc... and adds more flexibility to deployments.

[codecov]

Codecov Report

Merging #1548 into master will decrease coverage by 0.01%.
The diff coverage is 90.76%.

[cicdw]

minor name change tweaks, etc. -- this is a great addition to our environment library!!

[cicdw]

💥