✨ Add a separate registry for workqueue metrics

[sonamkshenoy]

This PR addresses #2670

A separate registry has been created for work queue metrics, so that we can import just this registry directly as metrics.WorkqueueRegistry without getting loads of other unrelated metrics.
This retains the previous behaviour as all the metrics are still available in the main Registry.

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[troy0820]

/hold

This does allow the existing behavior while introducing the set of metrics you propose to a different registry. However, this does not allow this to be configurable in the init and set this to what you provided.

In the issue we discussed allowing this to take the defined metrics to be initialized to a new registry to not utilize the internal registry.

If what you need are the metrics defined by this package, to have it be provided to the new registry, is there a way we can do this on the consumer side where you can push them to where ever you want?

It sounded like the problem was you didn't want all the rest of the stuff and the things you did need, you wanted them in a different registry.

[sonamkshenoy]

Hey @troy0820

Yep, I need just the work queue related metrics in my application. So, in this case (which implements the approach 1), I could have these metrics directly as metrics.WorkqueueRegistry. And I won't need the metrics.Registry anymore.

If what you need are the metrics defined by this package, to have it be provided to the new registry, is there a way we can do this on the consumer side where you can push them to where ever you want?

I'm not sure there is a way I can do this? The init() function in this package gets called before the init() function in our application as it is being imported (and probably called first). Thus, even if we create our metrics, we can't register them with the work queue, unless we remove the SetProvider() function in the init() of this file.

[alvaroaleman]

I understand the problem, but this means that the workqueue metrics will disappear for all existing users. That is not an option. We need to find a solution that does not break existing users.

/hold

[sonamkshenoy]

Hey @alvaroaleman , these metrics won't disappear actually. We are adding those metrics back to the main Registry with Registry.Register(WorkqueueRegistry). So this won't affect anything for existing users.

[sonamkshenoy]

Hey @troy0820 @alvaroaleman

There are 2 more options I could think of:

1. Just capitalise the metrics in this file workqueue.go without any other additions in the code, so that they can be exposed for use to users who can register them with their registry. [Would there be any issue with this?]
2. Functionality for users to register metrics of their choice as in ✨ Allow users to create custom registries #2672. I guess this is what @troy0820 was referring to?

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