[RelayMiner]: add proxy.Ping(...) capability to test connectivity between relay servers and backend URLs

[eddyzags]

Summary

This PR adds the capability to test the connectivity between the Relay Servers and the Backend URLs in two ways.

1. Safeguard at Startup:
   For every suppliers.[].service_config.backend_url referenced as input inside the Relay Miner Configuration file, the Relay Proxy will verify wether the network connection between the targeted backend_url and the relayerminer process is functioning properly. If one or more connections aren't possible, the relay miner won't be able to start.

2. Configurable Ping HTTP server:
   The Relay Miner process will listen for incoming request to synchronously test the connectivity of every referenced suppliers.[].service_config.backend_url. If one or more backend URLs aren't reachable, the incoming request will fail.

Based on the serverConfig.ServerType (Example: HTTP), each Server Type will implement their own logic to implement to test the connectivity.

Issue

• [RelayMiner] Add an ability to test RelayMiner configuration without application #447

Type of change

Select one or more:

• New feature, functionality or library
• Bug fix
• Code health or cleanup
• Documentation
• Other (specify)

Testing

Documentation changes (only if making doc changes)

• make docusaurus_start; only needed if you make doc changes

Local Testing (only if making code changes)

• Unit Tests: make go_develop_and_test
• LocalNet E2E Tests: make test_e2e
• See quickstart guide for instructions

PR Testing (only if making code changes)

• DevNet E2E Tests: Add the devnet-test-e2e label to the PR.
  • THIS IS VERY EXPENSIVE, so only do it after all the reviews are complete.
  • Optionally run make trigger_ci if you want to re-trigger tests without any code changes
  • If tests fail, try re-running failed tests only using the GitHub UI as shown here

Sanity Checklist

• I have tested my changes using the available tooling
• I have commented my code
• I have performed a self-review of my own code; both comments & source code
• I create and reference any new tickets, if applicable
• I have left TODOs throughout the codebase, if applicable

Summary by CodeRabbit

Summary by CodeRabbit

• New Features

  • Introduced a new configuration section for the ping functionality, allowing users to test backend connectivity within the relay miner's setup.
  • Added methods to handle ping requests, enhancing health check capabilities for relay servers.

• Bug Fixes

  • Improved error handling during the server startup process if any relay server is unreachable.

• Tests

  • Added tests for the new ping functionality to ensure operational integrity and reliability of the relay miner.