CBG-3736: delta sync for cv

[gregns1]

CBG-3736

• Store CV (In CBL format) on the DocumentDelta (this needs to be stored alongside the ToRevID on the delta for future backwards compatibility reasons)
• DocumentDelta needs now also stores history in CBL string format
• When subprotocol version is below v4 and delta sync is requested, fall back to sending full revision
• GetDelta: fromRevision switch the fetch from rev cache for this revision from using revID to CV, If delta is found on fromRevision we now check if this delta correlates to the top the CV we want the delta for, toRevision: switch the fetch from rev cache to use CV rather than revID
• UpdateDelta: has a CV version entitled UpdateDeltaCV which uses the CV code path to update a delata on revcache
• newRevCacheDelta: grabs HLV history off documentRevision and store in onto RevisionDelta for ease of sending to CBL inside sendDelta function
• processRev: Switch to get by CV from revcache for deltaSrcRev

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/2735/