(Blooms) Add metrics to compactor

[salvacorts]

What this PR does / why we need it:
This PR adds new metrics to the bloom-compactor:

• loki_bloomcompactor_compactions_started: Total number of compactions started
• loki_bloomcompactor_compactions_completed: Total number of compactions completed. With status (success, failure).
• loki_bloomcompactor_compactions_time_seconds: Time spent during a compaction cycle. With status (success, failure).
• loki_bloomcompactor_tenants_discovered: Number of tenants discovered during the current compaction run.
• loki_bloomcompactor_tenants_skipped: Number of tenants owned by this instance.
• loki_bloomcompactor_tenants_skipped: Number of tenants skipped since they are not owned by this instance.
• loki_bloomcompactor_tenants_started: Number of tenants started to process during the current compaction run.
• loki_bloomcompactor_tenants_completed: Number of tenants successfully processed during the current compaction run. With status (success, failure).
• loki_bloomcompactor_tenants_time_seconds: Time spent processing tenants.
• loki_bloomcompactor_tenants_series: Number of series processed per tenant in the owned fingerprint-range.

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
  • If the change is worth mentioning in the release notes, add add-to-release-notes label
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR