mimirtool: Add new migrate-utf8 command

[grobinson-grafana]

What this PR does

This commit adds a new migrate-utf8 command to mimirtool to migrate Alertmanager configurations for UTF-8 strict mode. It includes updated docs on how to use the command and validate its output.

Which issue(s) this PR fixes or relates to

Fixes #

Checklist

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

[gotjosh]

LGTM

Can you please add a changelog entry?

[jdbaldry]

In general, it's better to keep documentation timeless and instead keep changes and announcements to release notes or changelogs.

Is it possible that this can be rewritten to be timeless documentation?

If not, do we know when this will no longer be "new" and need preparation? For example, will it be the "normal" state of things in the next release of Mimir or perhaps the one after that?

It will be important to update the documentation to reflect that once we hit that time.

[grobinson-grafana]

In general, it's better to keep documentation timeless and instead keep changes and announcements to release notes or changelogs.

Is it possible that this can be rewritten to be timeless documentation?

Hmm, I'm not sure, let's see if we can? The docs here describe a one time command some Mimir users will need to run, depending on the state of their current configuration. This command is not really for Mimir server owners, but the tenants in those servers. If release notes and CHANGELOG.md is the best place for that then I'm happy to go with whatever works.

If not, do we know when this will no longer be "new" and need preparation? For example, will it be the "normal" state of things in the next release of Mimir or perhaps the one after that?

It will be important to update the documentation to reflect that once we hit that time.

The transition period is going to be ~6 months, after that, the backwards compatible code will be removed. If a tenant has not prepared their configuration before that time then their Alertmanager configuration may stop working, depending on whether it had any incompatible matchers in the first place.

[grobinson-grafana]

I had to rebase main due to a conflict in go.mod.

[jdbaldry]

Docs look great to me, thank you!

Perhaps a maintainer can advise where we should announce the breaking change to make sure that it is properly communicated.

[gotjosh]

Perhaps a maintainer can advise where we should announce the breaking change to make sure that it is properly communicated.

Hi Jack! There's no breaking change... yet. We're planning on making strict mode turned on by default in a couple of versions but we've plenty of time before that change is made.

[gotjosh]

I'm going to proceed with the merging of this as we have customers that are waiting to use this - please do let @grobinson-grafana know if there's more feedback he should address in a further PR @jdbaldry and @56quarters