Expose ingest storage config doc and changelog

[pracucci]

What this PR does

The Kafka-based ingest storage is still experimental, but we're moving closer to start running it in few production clusters at Grafana Labs. I think it's the right time to include it in the auto-generated config and, from now on, to mention changes to the CHANGELOG.

I've added the CHANGELOG entry under main / unreleased branch, even if it's not technically correct, because all changes are included in v2.13.0-rc.0. I'm open to feedback on how to handle it. The reason why I've written it under main / unreleased is because we haven't publicly mentioned it yet, but will be mentioned as experimental feature in the next release (so 2.14).

Which issue(s) this PR fixes or relates to

N/A

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.

[pstibrany]

I'm fine adding it to unreleased section, since all the options are still hidden in 2.13.

I'd suggest documenting the following mixin config options:

• ingest_storage_enabled -- enables alerts for ingest-storage
• show_ingest_storage_panels -- shows ingest-storage panels

[pracucci]

Thanks @tacole02. I should have addressed all your comments.

[pstibrany]

I'm fine adding it to unreleased section, since all the options are still hidden in 2.13.

I'd suggest documenting the following mixin config options:

• ingest_storage_enabled -- enables alerts for ingest-storage
• show_ingest_storage_panels -- shows ingest-storage panels

I meant documenting them in the changelog. However show_ingest_storage_panels is already mentioned in the changelog. ingest_storage_enabled comes from #7867, which is missing changelog entry, but alerts that it enables are already documented in

* [ENHANCEMENT] Alerts: add the following alerts when using ingest-storage: #7699 #7702
  * `MimirIngesterLastConsumedOffsetCommitFailed`
  * `MimirIngesterFailedToReadRecordsFromKafka`
  * `MimirIngesterKafkaFetchErrorsRateTooHigh`
  * `MimirStartingIngesterKafkaReceiveDelayIncreasing`
  * `MimirRunningIngesterReceiveDelayTooHigh`
  * `MimirIngesterFailsToProcessRecordsFromKafka`
  * `MimirIngesterFailsEnforceStrongConsistencyOnReadPath`

entry.

[pracucci]

ingest_storage_enabled comes from #7867, which is missing changelog entry, but alerts that it enables are already documented in entry.

I retro-actively added the PR number to that entry.