Do not add multiple copies of stale docs to Lucene

[dnhatn]

Since #29679 we started adding stale operations to Lucene to have a complete history in Lucene. As the stale docs are rare, we accepted to have duplicate copies of them to keep an engine simple.

However, we now need to make sure that we have a single copy per stale operation in Lucene because the Lucene rollback requires a single document for each sequence number.

Relates #31637

[elasticmachine]

Pinging @elastic/es-distributed

[dnhatn]

@bleskes This PR is to deal with the duplicated - nested documents. The rollback won't be correct without this deduplication logic in the following scenario.

1. Indexing a nested document
2. That nested document arrives again (might happen during recovery + replication), and will be added to Lucene as stale
3. Delete that nested documents
4. Rollback the deletion in step 3. With the current implementation, we don't know how to rollback precisely a single copy of that nested document.

[bleskes]

we discussed this via another channel and agreed we need to spend some thought on whether this is needed.

[jasontedor]

@dnhatn I think that we can close this PR for now?

[dnhatn]

@jasontedor Thanks for the ping. Yes, I should have closed it.

I am closing this as we are going to implement a commit-based rollback.