KV PurgeDeletes should keep "recent" markers

[kozlovic]

Overview

For libraries that provide the maintenance function PurgeDeletes(), this should be enhanced to follow this algorithm:

• Create a "watcher all" (subject is ">")
• Iterate through entries, if entry is a DEL or PURGE, add this entry to a list
• After getting the last entry, for through the list of "delete markers". If the marker is older than a certain threshold (default 30 minutes), then purge the stream by subject. If the marker is recent, purge the stream by subject, but add the "Keep:1" to the stream purge request, so that we keep the marker.

There is no ADR for that since PurgeDeletes() is not part of the core API.

Clients and Tools

• Go @wallyqs
• Java @scottf
• JavaScript @aricart
• .Net @ColinSullivan1 @scottf
• C @kozlovic
• Python @wallyqs
• Ruby @wallyqs
• Rust @Jarema

Other Tasks

• docs.nats.io updated
• Update ADR to Implemented
• Update client features spreadsheet

Client authors please update with your progress. If you open issues in your own repositories as a result of this request, please link them to this one by pasting the issue URL in a comment or main issue description.