DDLServiceMgr can take long time to build partitioned index with replica

DDLServiceMgr triggers the build of a partitioned index with replica created in non-defer mode. In order to do this, it needs MetadataProvider.

When DDLServiceMgr tries to instantiate a new MetadataProvider, it waits for 500ms.
https://github.com/couchbase/indexing/blob/457f86ae37854d1a7cf34ef7df6df6e723c28548/secondary/indexer/ddl_service_manager.go#L1657

In case of large number of indexes, 500ms may not be enough, as there are other consumers such as getLocalIndexMetadata (used to respond to /getIndexStatus) which take lock while iterating over the repo.

This can delay the index build.