[Utility] Support RESTful relays (need to merge #960 first)

[adshmh]

Description

This PR adds support for relays in REST format, i.e. with JSON payload rather than JSONRPC, and optionally specify a Path and the HTTP Method.

Issue

Part of work on #860

Type of change

Please mark the relevant option(s):

• New feature, functionality or library
• Bug fix
• Code health or cleanup
• Major breaking change
• Documentation
• Other

List of changes

• Update RPC structs and handlers to support REST
• Update client binary to handle REST
• Update Servicer logic to handle REST

Testing

• make develop_test; if any code changes were made
• make test_e2e on k8s LocalNet; if any code changes were made
• e2e-devnet-test passes tests on DevNet; if any code was changed
• Docker Compose LocalNet; if any major functionality was changed or introduced
• k8s LocalNet; if any infrastructure or configuration changes were made

Required Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added, or updated, godoc format comments on touched members (see: tip.golang.org/doc/comment)
• I have tested my changes using the available tooling
• I have updated the corresponding CHANGELOG

If Applicable Checklist

• I have updated the corresponding README(s); local and/or global
• I have added tests that prove my fix is effective or that my feature works
• I have added, or updated, mermaid.js diagrams in the corresponding README(s)
• I have added, or updated, documentation and mermaid.js diagrams in shared/docs/* if I updated shared/*README(s)