Add filtering to KV keys retrival method

[Jarema]

Overview

keys() method returns all keys in KV. As KV buckets grow, it makes sense to be able to filter them out.

The behavior is documented in ADR-8, specifically https://github.com/nats-io/nats-architecture-and-design/blob/main/adr/ADR-8.md?plain=1#L139

Clients and Tools

• [ ] CLI @ripienaar
• [ ] Go @piotrpio
• [x] Java @scottf https://github.com/nats-io/nats.java/pull/1173
• [ ] JavaScript @aricart
• [x] .Net @scottf https://github.com/nats-io/nats.net/pull/907
• [ ] C @levb
• [ ] Python @caspervonb
• [ ] Ruby @wallyqs
• [ ] Rust @Jarema
• [x] .NET V2 @mtmk - https://github.com/nats-io/nats.net.v2/pull/545

Other Tasks

• [ ] docs.nats.io updated @bruth
• [ ] 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.

[saurabhojha]

@levb Would be grateful for a review on this pr : https://github.com/nats-io/nats.c/pull/797