Alerting: Create new state history "fanout" backend that dispatches to multiple other backends at once (#64774)
* Rename RecordStatesAsync to Record
* Rename QueryStates to Query
* Implement fanout writes
* Implement primary queries
* Simplify error joining
* Add test for query path
* Add tests for writes and error propagation
* Allow fanout backend to be configured
* Touch up log messages and config validation
* Consistent documentation for all backend structs
* Parse and normalize backend names more consistently against an enum
* Touch-ups to documentation
* Improve clarity around multi-record blocking
* Keep primary and secondaries more distinct
* Rename fanout backend to multiple backend
* Simplify config keys for multi backend mode
(cherry picked from commit a31672fa40)
Co-authored-by: Alexander Weaver <weaver.alex.d@gmail.com>
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