Investigate non aligned snapshot at the end of mutation load

Discovered while running the tests locally for MB-20188. In one of the test runs, the mutation load finished but the last snapshot was not snap aligned. This resulted in timekeeper marking the timestamp to be NO_SNAP type. This is not expected as at the end of the load, all vbucket seq nums should be snapshot aligned. This can lead to some of the mutations not being available in the last snapshot.

Logs are attached.

Test case:

./testrunner -i b/resources/dev-4-nodes-xdcr_n1ql_2i.ini initial_index_number=3,get-cbcollect-info=True -t 2i.memdb_oom_2i.SecondaryIndexMemdbOomTests.test_oom_increase_mem_quota,gsi_type=memory_optimized,nodes_init=4,services_init=kv:n1ql-kv-index-index,doc_ops=True,standard_buckets=2,default_buckets=1,initial_index_number=4,scan_consistency=request_plus,skip_cleanup=True