CBG-3807: Diagnostic API - GET user/doc access endpoint

[mohammed-madi]

CBG-3807

Describe your PR here...

• Add an endpoint under the diagnostic API for getting a user's access spans for a document or number of documents
• the url is /{keyspace}/_user/(username}?docids={docid},{docid}
• added tests
• Fixed all user channels endpoint not getting a deleted role's channel history

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
• [ ] Update Go module dependencies when merged

Integration Tests

• [ ] GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/2520/

[github-actions[bot]]

Redocly previews

• Admin API
• Public API
• Metric API
• Diagnostic API