mimirpb: export IsClientErrorCause() function

[duricanikolic]

What this PR does

This PR exports mimirpb.IsClientErrorCause() function, that distinguishes between mimirpb.ErrorCauses corresponding to client and server errors. Currently, mimirpb.BAD_DATA is the only mimirpb.ErrorCause corresponding to client errors.

This PR makes no semantical change, it just exports the error cause check already used within mimirpb.IsClientError().

Checklist

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

[replay]

Approved because this doesn't change any logic.
I still think it's weird that for example METHOD_NOT_ALLOWED is defined to not be a client error here, but that's a separate discussion outside the scope of this PR.

[narqo]

I still think it's weird that for example METHOD_NOT_ALLOWED is defined to not be a client error

In #7618 we had a somewhere long discussion on if ours gRPC METHOD_NOT_ALLOWED should be mapped to HTTP 405 or 501. We landed up with the latter mainly because of how this specific error was used in Mimir's ingest-storage.

[colega]

Sounds like the problem is that METHOD_NOT_ALLOWED is a wrong name for that status code (because it's something that lives in a similar domain as HTTP, but has a completely different meaning from 405 Method Not Allowed).