Lay out a strategy for OpenAPI integration

This would've accelerated @f.mazeikis' work at ✨ [PP-1] Integrate saving sections with the backend Postponed by multiple days!

Also:

Add test coverage for \Drupal\experience_builder\Controller\ApiComponentsController this will also give us OpenAPI validation of the response

— @larowlan at 📌 Add test coverage for \Drupal\experience_builder\Controller\ApiComponentsController Active , emphasis mine.

Opened 📌 Handle all paths in OpenAPI request validation Active as a first step.