[Metrics Generator] Allow running on a different source of data

[flxbk]

What this PR does:

This PR makes it possible to run the metrics-generation features of metrics-generator (i.e. spanmetrics and service-graph processors, but not localblocks) on a different Kafka-compatible data source. It introduces two three new configuration options to achieve this:

1. DisableLocalBlocks: this defaults to false, when set to false there's no change in behavior. When this is set to true, metrics-generator will not run the localblocks processor even when it's configured for a tenant.

2. DisableGRPC: this defaults to false as well. When it's true the gRPC server setup is skipped and metrics generator doesn't join the generator ring (which it only needs to do to make itself available to be queried via gRPC, so when gRPC is disabled joining the ring makes no sense).

3. Codec: this controls what data type metrics generators expect to find in the Kafka records they consume. This PR adds support for consuming records that contain ptrace.Traces instead of the tempopb.PushBytesRequest that's already supported.

This PR also introduces a way of making metrics generator watch a configurable partition ring (currently watching the ingester ring is hardcoded).

Which issue(s) this PR fixes:
Fixes n/a

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[CLAassistant]

All committers have signed the CLA.

[yvrhdn]

Overall this looks good to me but I'll let someone with more experience on the new Kafka ingest and local-blocks processor look into it 🙂

[mapno]

I haven't done an in-depth review. Still have some comments.

[flxbk]

I have rebased to resolve conflicts with #4721 and tried to address all the PR feedback that has come in so far.

[joe-elliott]

The dependence between "no local blocks" and the partition ring watcher don't make sense to me. Shouldn't this be something like MetricsGeneratorPartitionRing

[flxbk]

In a different PR comment, @mdisibio suggested we could use a separate target for this metrics generator mode. That is what I did here, however that new mode still needs a way to watch a (configurable) partition ring, hence the dependency on GeneratorRingWatcher.

[mdisibio]

Thanks for the amount of work put into this. The final result with the dedicated target is working well to keep all of the unique bits together, and I think it gives a clean separation between the modes, so that we can continue to iterate on naming or other things without breaking config or deployment changes. LGTM

[flxbk]

Thanks for the review and all the suggestions that have helped me make this better!

I haven't added a changelog entry yet to avoid eternal rebases/conflicts with other entries, but happy to do that before this goes in.

[flxbk]

Added changelog and rebased to resolve conflicts in changelog.md.