chore/add concurrency support for deployments

[jimid27]

• Resolves: https://linear.app/prefect/issue/PLA-701/deployments-support-concurrency
• Adds concurrency limit which is an int and concurrency options which is an object
• Based on the current api docs for deployments found here

[mitchnielsen]

🤔 Looking into concurrency_limit more. Looks like it is deprecated in favor of concurrency_limit_id based on this code. That change was added in PrefectHQ/prefect#15426, which has a lot more context on the change. I need to read up on that to understand how we need to implement the ability in the Terraform provider.

The relevant docs (https://docs.prefect.io/v3/deploy/index#concurrency-limiting) still instruct you to set concurrency_limit directly, and the API docs don't say it's deprecated. And from the UI it looks like the deprecated option is still in use:

I'll read up more and reach out to the backend folks if anything needs clarification.

PrefectHQ/prefect#15426 (comment):

Note that you can still access deployment.concurrency_limit but it's now deprecated so it emits a warning on access and also it will be None.

This explains why the tests here were failing for me, saying we set 1 but the result came back as 0.

Overall: looks like this field is going away next month (Dec 2024), so we probably want to implement the newer approach.

Further reading:

• https://docs.prefect.io/v3/develop/global-concurrency-limits
• https://docs.prefect.io/v3/deploy/index#concurrency-limiting
• Docs for deployment concurrency limits prefect#15527