Storage: Watch support (#82282)

* initial naive implementation

* Update pkg/services/store/entity/sqlstash/sql_storage_server.go

Co-authored-by: Igor Suleymanov <radiohead@users.noreply.github.com>

* tidy up

* add action column, batch watch events

* initial implementation of broadcast-based watcher

* fix up watch init

* remove batching, it just adds needless complexity

* use StreamWatcher

* make broadcaster generic

* add circular buffer to replay recent events to new watchers

* loop within poll until all events are read

* add index on entity_history.resource_version to support poller

* increment r.Since when we send events to consumer

* switch broadcaster and cache to use channels instead of mutexes

* cleanup

---------

Co-authored-by: Igor Suleymanov <radiohead@users.noreply.github.com>

pkg/plugins/backendplugin/secretsmanagerplugin/secretsmanager_grpc.pb.go

@@ -1,7 +1,7 @@
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
 // - protoc-gen-go-grpc v1.3.0
-// - protoc             v4.25.1
+// - protoc             v4.25.2
 // source: secretsmanager.proto
 
 package secretsmanagerplugin