Plugins: Refactor kvstore usage in signing keys and angular patterns (#73154)

* Initial refactoring work for plugins kvstore

* Replace implementations for keystore and angularstore

* Cleanup

* add interface check

* lint

* fix storeKeyGetter not being called in namespacedstore set

* Fix tests

* Comments

* Add tests

* Fix invalid cap in ListKeys when store is empty

* Update docstrings

* Add setLastUpdatedOnDelete

* Renamed DefaultStoreKeyGetterFunc, add TestDefaultStoreKeyGetter

* Sort imports

* PR review: removed last_updated key

* PR review: Removed setLastUpdatedOnDelete

* Re-added relevant tests

* PR review: Removed SingleKeyStore

* PR review: Removed custom marshaling support

* Renamed marshaler.go to marshal.go

* PR review: removed unused interfaces

* PR review: Moved marshal into namespacedstore.go

* PR review: removed storekeygetter

* Removed unused file cachekvstore.go

* Renamed NamespacedStore to CacheKvStore

* removed todo

pkg/services/pluginsintegration/keyretriever/dynamic/dynamic_retriever_test.go

@@ -79,7 +79,7 @@ func Test_PublicKeyUpdate(t *testing.T) {
 		defer v.lock.Unlock()
 		ti, err := v.kv.GetLastUpdated(context.Background())
 		require.NoError(t, err)
-		require.Less(t, time.Time{}, *ti)
+		require.Less(t, time.Time{}, ti)
 	})
 
 	t.Run("it should remove old keys", func(t *testing.T) {