Update GET /api/peers?limit=xxx&offset=yyy&state=zzz endpoint

[shuse2]

Description

Add the endpoints:

• GET /api/peers?limit=xxx&offset=yyy&state=zzz

according to the following specification:

• It should return decoded peers
• Validate if limit and offset are valid numbers
• Validate if state is either connected or disconnected
• If query params are not specified, it should default to limit=100, offset=0, state=connected

Motivation

The HTTP API should return the stored peers in the attached node.

Acceptance Criteria

• Add unit tests
• Register plugin to core, and check if it returns decoded data
• Check if invalid query returns 400 with error message

Additional Information

Related issues: #5213