block-builder: Add basic series limit

[codesome]

What this PR does

This is a very naive solution to the limits before we have a better solution.

With this PR, we will allow up to the global series allowed for the user per partition, iff they global limit is under block-builder.apply-global-series-under. We do not apply any limits if the configured limit is over the flag value.

Few examples of it working:
Let's assume block-builder.apply-global-series-under=10000

1. If a user has global limit of 5k series, and is sharded between 3 partitions, then it will allow 5k series per partition. So technically this user can ingest up to 15k series.
2. If a user has global limit of 5k series, and is sharded only on 1 partition, then with 5k series per partition, the user will be limited to 5k series as intended.
3. If a user has global limit of 15k series, and no matter how many partitions they are sharded to, while ingesters will apply the proper limits, block builder will not apply any limits (meaning they can ingest anything).

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.

[pracucci]

I only checked the config to see the overall idea of this change (which LGTM). I let rest of the team reviewing the actual code changes.

[seizethedave]

LGTM modulo commentary 😸

[seizethedave]

I realize this is a temporary measure, but Under doesn't match with <=. It's really an AtMost. Perhaps applyGlobalSeriesLimitMax?

[codesome]

With the reword to applyMaxGlobalSeriesPerUser..., using Max as a suffix again sounds odd. How about applyMaxGlobalSeriesPerUserBelow? And put in comments that it is inclusive.

[codesome]

@seizethedave I updated the PR. PTAL.