Enable -ingester.error-sample-rate by default and promote from experimental to advanced

[pracucci]

What this PR does

At Grafana Labs, we're running Mimir with -ingester.error-sample-rate=10 since several months and we're happy with it. I think it's a reasonable default for Mimir, so I suggest to enable the ingester error sampling by default and promote the feature from experimental to advanced.

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.

[jdbaldry]

Do we talk about logging behavior anywhere in the docs that we should consider including this information in? Does it justify formal documentation beyond the reference material?

[pracucci]

Do we talk about logging behavior anywhere in the docs that we should consider including this information in? Does it justify formal documentation beyond the reference material?

@jdbaldry You raised a good point! I think we should document it in our runbooks. Please take a look at the changes I did.

Note: I also grepped "log" in the rest of the doc and I haven't find any other place where we explicitly mention logs like we do in runbooks.

[jdbaldry]

Nice! Thanks for thinking about where this might need to be documented, I think the extra documentation is a useful reminder in the runbooks :)