Bugfixes

• [BUGFIX] metrics-generator: don't inject X-Scope-OrgID header for single-tenant setups 1417 (@kvrhdn)
• [BUGFIX] compactor: populate compaction_objects_combined_total and tempo_discarded_spans_total{reason="trace_too_large_to_compact"} metrics again 1420 (@mdisibio)
• [BUGFIX] distributor: prevent panics when concurrently calling shutdown to forwarder's queueManager 1422 (@mapno)