* Add "debouncer" queue, which can combine incoming elements. * Rebuild indexes asynchronously. * Remove duplicate method. * Fix bleve tests. * Extracted combineRebuildRequests and added test for it. * Add TestShouldRebuildIndex * Added TestFindIndexesForRebuild * Added TestFindIndexesForRebuild * Introduce index_rebuild_workers option. * Add metric for rebuild queue length. * Add TestRebuildIndexes. * Fix import. * Linter, review feedback.