[CX] Analytics doesn't persist DCP snapshot markers

CBAS doesn't persist snapshot markers with the DCP state. This could lead to missing some docs in CBAS due to de-duplication by the DCP producer. Here is the scenario when that can happen:

Consider a single vbucket stream. the stream starts with a snapshot marker from 1-1000

The mutation with sequences 1 and 1000 both were upserts on the same key.

Due to de-duplication, we don't see the first mutation, and when we reach sequence number 1000, we would see the new mutation. If we crash in between, say at sequence number 500 and kv performs a rollback at that exact point, we hit the problem.

Assume that we come back up and we find that we have persisted upto seq number 500 and so, we currently, re-open the stream from 500, with snapshot marker 500,500. To KV, this means that we have seen the mutation at sequence number 1 and so, there is no need to rollback.

We would continue assuming that we have all the docs but that is not correct.