CBG-4440: HLC implementation for blip tester client

[gregns1]

CBG-4440

• HLC implementation for value in CV for blip tester client
• Using rosmar implementation now, so not ready to merge until rosmar is merged (this PR points to that PR in go mod)

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

Dependencies (if applicable)

• Link upstream PRs: make hlc public for use in blip client tester in sync gateway couchbaselabs/rosmar#45
• Update Go module dependencies when merged

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/2967/

[bbrks]

This is good as-is - just wondering whether we can move the rosmar implementation into a location that can be used by both?