Add alert_relabeling_configs and external_labels to mimir ruler

[ToonTijtgat2]

What this PR does

Add the ability to have alert_relabeling_configs and external_labels.

Which issue(s) this PR fixes or relates to

Fixes #7295 Fixes https://github.com/grafana/mimir/issues/3490

Checklist

• [ ] Tests updated.
• [x] Documentation added.
• [x] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX].
• [ ] about-versioning.md updated with experimental features.

[CLAassistant]

All committers have signed the CLA.

[ToonTijtgat2]

Dear

Thanks for checking this pullrequest. To be honest I wanted to be able to have an overwrite on the external label or alert_relabel_configs setup per tenant (UserId) I did not find how to do this. Think limits should be included in the ruler setup, The default NewDefaultMultiTenantManager does not take any userid in account.

Toon Tijtgat

[ToonTijtgat2]

The code between loki and mimir is different, but I think this is optional to do in loki according to this line of code. https://github.com/grafana/loki/blob/46c6118eb2a2d56406042431dfbed288df6e924b/pkg/ruler/base/manager.go#L202

Would it be possible to implement this option for mimir?

[dimitarvdimitrov]

@grafana/mimir-ruler-and-alertmanager-maintainers can one of you folks take a look at this PR please?

[arnitolog]

@dimitarvdimitrov are there any plans to merge this PR? we are looking forward to this functionality.

[ToonTijtgat2]

i'm not terribly familiar with the ruler's flow of updating rules. I think this needs some basic tests at least. Perhaps extending TestSendAlerts in ruler_test.go? I'm not super sure

I've also pinged the alerting team in slack to see if they can give this a look

Thanks for checking. As suggested I moved the changelog to the mimir section.

For the testing, I'm not sure how to handle this. I went to the code of loki to see how they handled it there, https://github.com/grafana/loki/blob/main/pkg/ruler/base/ruler_test.go But I'm not able to find anything related to those labels.

[duricanikolic]

The CHANGELOG has just been cut to prepare for the next Mimir release. Please rebase main and eventually move the CHANGELOG entry added / updated in this PR to the top of the CHANGELOG document. Thanks!

[QuentinBisson]

I just find this and we would really be interested in this

[dimitarvdimitrov]

@grobinson-grafana can you take a look at this PR please?

[QuentinBisson]

@dimitarvdimitrov is there a way to help push this forward? I really think this would provide a lot of value

[QuentinBisson]

@duricanikolic do you know if it's possible to get this PR forward? This is a really important feature