feat: HTTP REST API: Filter

[jm-clius]

Background

This forms a subtask of #1076.
Nwaku nodes operating as 12/WAKU2-FILTER clients can use the filter protocol to subscribe to service nodes to receive messages adhering to a set of subscription criteria.
Currently these filter operations can only be triggered in clients in an internal Nim API call.
Although there exists an external filter client JSON-RPC API, this was designed for a deprecated version of the filter protocol. There is therefore no external API for filter client calls.
The JSON-RPC API is clunky to use and call signatures outdated. As such, we've started migrating to an HTTP REST API.

Suggested solution

Create and expose a Filter Client HTTP REST API functionality. It should use the existing REST APIs as inspiration and follow the same patterns and structure. Although, the JSON-RPC API can be referred to, the new API method should follow the new filter API specifications to construct the calls.

Acceptance criteria

• working HTTP Filter Client REST API to perform filter client operations on remote service nodes
• sufficient unit tests for basic functionality
• integration of Filter Client API into the wakunode2 app