Compact userTSDB's OOO head when compacting head

[npazosmendez]

What this PR does

This adds a call to db.CompactOOOHead as part of userDb.compactHead, which means the OOO head is also compacted apart from the in-order head. As a consequence, compactions caused by idling DBs or forced head compactions will now also compact the OOO head, see code below:

mimir/pkg/ingester/ingester.go

Lines 2196 to 2203 in 6852e94

	case force:
	reason = "forced"
	err = userDB.compactHead(i.cfg.BlocksStorageConfig.TSDB.BlockRanges[0].Milliseconds())
	case i.compactionIdleTimeout > 0 && userDB.isIdle(time.Now(), i.compactionIdleTimeout):
	reason = "idle"
	level.Info(i.logger).Log("msg", "TSDB is idle, forcing compaction", "user", userID)
	err = userDB.compactHead(i.cfg.BlocksStorageConfig.TSDB.BlockRanges[0].Milliseconds())

Which issue(s) this PR fixes or relates to

Fixes #4160

Checklist

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

[CLAassistant]

All committers have signed the CLA.

[pstibrany]

This looks fine to me. Let's fix the test and get this merged.

This PR also needs a CHANGELOG entry.

[npazosmendez]

@pstibrany thanks for the feedback, test looks cleaner now. I've added a changelog entry, but you may be able to phrase it better since you have more context on the issue this was causing. Feel free to push any changes and merge if you think it's ready (I'll be on PTO for the rest of the week and I don't want to block this)

[pstibrany]

Thank you very much. I've rephrased changelog entry a bit, but we cannot merge until you sign the Contributor License Agreement: https://cla-assistant.io/grafana/mimir?pullRequest=4180.

I've enabled automerge, once you sign the CLA.

[jesusvazquez]

Nice work!! 💪

I believe this PR has also helped with #4160