create index snapshot metadata object only if collection data has changed

Create index snapshot metadata object only if collection data has changed. This has a couple of benefits:

1. The index snapshot metadata objects do not need to be created for all the indexes on a bucket. Rather, the cost only needs to be paid for collections where the data has changed. This helps with the scalability.

2. Indexer doesn't need to use strict consistency mode due to mismatch between bucket vs collection seqnum(MB-42655).