Add "remote read", "metadata", and "exemplar" queries to "Mimir / Overview" dashboard

[pracucci]

What this PR does

Looking at the "Mimir / Overview" dashboard in production, I've noticed a good amount of queries fall into the "other" group. In this PR I'm adding dedicated grouping for "remote read", "metadata", and "exemplar" queries.

Which issue(s) this PR fixes or relates to

N/A

Checklist

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