CBG-4257 add HLV into BlipTesterCollectionClient

[torcolvin]

I created AddHLVRev in addition to AddRev since there would be a lot of places where code would need to change. I have a proposed refactor to drop the error arg out of AddRev and I could evaluate whether we would want to change the signature everywhere in rest package and not just topology tests.

My initial revision of this PR put HLV into DocVersion but Ben convinced me not to do this because DocVersion is used as a map key in blip tester, which breaks some semantics. Additionally, we use DocVersion to abstract CV/revtree id only, so adding HLV means that you could end up with two versions where the cv was the same, but one would have a PV. This version is also a lot simpler.

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/2876/