Unified Storage/Search: Add max count config for indexing (#107255)

* Add max count config for indexing
* Build empty index when max count is exceeded
* Address linting
* Refactor buildIndexes
* Add test for max count threshold
* Update test doc comments
* Refactor TestBuildIndexes_MaxCountThreshold to not use mock framework
* Rename mocks used in TestBuildIndexes_MaxCountThreshold

* Refactor mockResourceIndex

* Test setting of indexing threshold configs

* Tweak comments, log

* Fix logging in buildEmptyIndex

* Export and reuse TestDocumentBuilderSupplier

* Reuse MockResourceIndex

pkg/setting/setting.go

@@ -563,6 +563,7 @@ type Cfg struct {
 	IndexMaxBatchSize                          int
 	IndexFileThreshold                         int
 	IndexMinCount                              int
+	IndexMaxCount                              int
 	IndexRebuildInterval                       time.Duration
 	IndexCacheTTL                              time.Duration
 	EnableSharding                             bool