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
• Java @scottf Add filtering to KV keys methods nats.java#1173
• JavaScript @aricart
• .Net @scottf https://github.com/nats-io/nats.net/pull/907
• C @levb
• Python @caspervonb
• Ruby @wallyqs
• Rust @Jarema
• .NET V2 @mtmk - Add KV Filtering of keys nats.net#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 :
nats-io/nats.c#797