feat: add config parameters to toggle WAL concurrency and timeouts

[danxmoran]

Closes #21600

I've split the changes into 3 commits to (hopefully) help review:

1. Adds the context parameter to the Take method, and updates the unit tests for limiter.Fixed to show its effects
2. Updates our storage code to plumb a context through to every usage of Take
3. Adds a bunch of context.Background args to all the methods that need it in our tests

[williamhbaker]

Nothing else from my end! Interested to see what @lesam thinks as well.

[lesam]

I haven't fully reviewed the plumbing but the overall approach seems fine. It's actually much more extensive than expected but seems like a good move to use contexts for cancellation and propagate it up the API.

I was expecting us to also add an explicit WithTimeout to the WAL writing path - does the PR accomplish that?

[danxmoran]

I was expecting us to also add an explicit WithTimeout to the WAL writing path - does the PR accomplish that?

I'll double-check if we're already setting any timeouts on the write-path, and add one if not.

[danxmoran]

@lesam @wbaker85 ready for another look

[williamhbaker]

Nothing else on my end!