Implement client credentials flow in CLI, centralize managing config

Overview

The CLI tool needs to be able to send HTTP requests to the relevant API endpoints, and be authenticated via the solution introduced in #3525572: Implement OAuth2 authentication for API endpoints related to code components.

→ See: #3525571: [Meta] CLI tool for code components

Proposed resolution

1. Read the documentation on how to set up consumers produced in #3525572: Implement OAuth2 authentication for API endpoints related to code components.
2. Implement reading the followings from environment variables or a .env file — e.g., using dotenv:
   1. Drupal site base URL
   2. Client ID
   3. Client secret
3. Use an OAuth2 client library implemented in Node.js, make the CLI tool execute a single HTTP request to /api/v0/config/js_component, and simply print the results. Use the /oauth/token route to retrieve an access token.