CBG-3467 add verbose mode for _all_dbs

[torcolvin]

• Use a query parameter to show verbose view of databases.
• Used oneOf to specify this - this is how it renders in redocly: https://redocly.github.io/redoc/?url=https://raw.githubusercontent.com/couchbase/sync_gateway/b62b000ed6cce3b069c8b3d1beafe1f0e40035c8/docs/api/admin.yaml#tag/Database-Management/operation/get__all_dbs
• removed HEAD from redocly since it is not that helpful and I updated the description and I decided to just drop it off.

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

[bbrks]

LGTM - will leave for @JRascagneres to have final say/merge

[JRascagneres]

Yeah think it looks fine, as you said a sort might be nice?

[bbrks]

Looks OK but may want to consider sort.Slice to avoid building the intermediate slice for sorting.

I expect this is an endpoint the UI will be polling on a very regular inteval like it does for /_resync, etc.

[adamcfraser]

Looks good, minor docs suggestions.

Comments have been addressed.