max_global_traces_per_user: take into account ingestion.tenant_shard_size when converting to local limit

[kvrhdn]

What this PR does:
Fixes an oversight when adding ingester shuffle sharding support (#3506).

max_global_traces_per_user is a global limit enforced in the ingester. It is converted to a local limit by dividing the global limit by the amount of (healthy) ingesters in the ring. When ingestion.tenant_shard_size is set the tenant will have a smaller ring than the total count of ingesters. As a result the actual local limit would be higher in those cases.

Before:

actual local limit = max_global_traces_per_user / ingester instances

After:

actual local limit = max_global_traces_per_user / min(ingester instances, tenant_shard_size)

Which issue(s) this PR fixes:
Fixes #

Checklist

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

[mapno]

Nice fix

[electron0zero]

good catch