Improve replication layer docs to speak about raft strong consistency

[awoods187]

Andy Woods (awoods187) commented:

Improve https://www.cockroachlabs.com/docs/stable/architecture/replication-layer.html#raft to discuss how CRDB uses raft replication to enforce strong consistency as opposed to eventual consistency. cc @nvanbenschoten

Jira Issue: DOC-409

[jseldess]

@awoods187, can you say more about the nature of the improvements you'd like to see?

[awoods187]

it was in response to https://twitter.com/samedguener/status/1214822875829592064?s=20

@nvanbenschoten and I were chatting about it and we realized we didnt have anything that explained this in detail to send with a reply along the thread. From my conversation he shared:

We talk about serializable a lot but serializable isn’t really related to eventual consistency they’re on two different axis. The first is an isolation level, the second is s a consistency level. Cockroach uses Raft replication to enforce strong consistency. 

I think it'd be useful to expand upon this a bit more. Perhaps a strong consistency vs. eventual consistency paragraph.

[jseldess]

Thanks, @awoods187.