Provide option to eagerly copy the new index files in CopyOnRead

Currently the CopyOnRead feature lazily starts copying the index files upon first access. This at times does not work efficiently because the index gets updated frequently and hence by the time copy is done index would have moved on. Due to this most of the index read turn out to be remote reads and cause slowness

We should provide an option on per index basis to enable copying the files eagerly before exposing the new index to the query engine such that any read done is done locally