#### What this PR does

Updates Mimir version to 3.1.0 in preparation for mimir-distributed
6.1.0.

#### Which issue(s) this PR fixes or relates to

Part of #14392 

#### Checklist

- [ ] Tests updated.
- [ ] Documentation added.
- [ ] `CHANGELOG.md` updated - the order of entries should be
`[CHANGE]`, `[FEATURE]`, `[ENHANCEMENT]`, `[BUGFIX]`. If changelog entry
is not needed, please add the `changelog-not-needed` label to the PR.
- [ ]
[`about-versioning.md`](https://github.com/grafana/mimir/blob/main/docs/sources/mimir/configure/about-versioning.md)
updated with experimental features.