Concurrency limit UX enhancements: add strict mode

[cicdw]

This PR deprecates create_if_missing which causes an ill-posed problem: creating a limit implicitly has no obvious default limit value.

Instead, the behavior we want is:

• taking concurrency from a limit name that doesn't exist in the backend should be functionally equivalent to taking concurrency from a limit name that has a limit of None or from a limit that is "inactive" and therefore - at this instant - might as well not exist, i.e., it allows execution without creating any new object in the backend (and we log a WARNING to alert users)
• for users who want stricter control, we have a new kwarg strict: bool that specifies whether to raise an error if the limit name doesn't exist in the backend; this defaults to False but can be set to True. Setting this to True is satisfying the need of "I really want to make sure I have full control over the circumstance in which this runs" and if the limit doesn't exist, we don't yet know those circumstances and so we prevent execution through a raised exception

I believe I need to revisit the docs for these utilities, but in the meantime wanted to get some eyes on the code.

[codspeed-hq]

CodSpeed Performance Report

Merging #15297 will not alter performance

_{Comparing create-if-missing-no-longer (d89faa1) with main (39a4f52)}

Summary

✅ 3 untouched benchmarks

[abrookins]

This all looks right to me! 👍

[zzstoatzz]

lgtm!

[zzstoatzz]

nice one heh