Goal

To be able to get the current configuration to check if expected features, gates are enabled and info is cached.

Summary
Implement a configuration model.

Consume it from config:show CLI command.

Offer alternative output (JSON document or a validator).

Plan

In T663#12745, @dereckson wrote:

• refactor config:show command to be only a controller to output a CLI view:
  • create a class to query configuration information
  • consume this class from the config:show code
• offer a web view from the configuration as a JSON document
• consider if it's more simple to offer a POST route to submit an expected config payload to answer VALID/INVALID instead
• ensure we can easily detect "projects map is not cached" issue