VSD Add feature tests for YAML configuration flow

The following discussion from !119108 (merged) should be addressed:

• @ekigbo started a discussion:

  💡 Thanks for adding all the jest tests to this @apennells, as a follow-up, I think it would be good to add some additional RSpec tests for this new functionality.

  I think most likely testing:

  • Successful Dashboard configuration via YAML
  • Editing an existing YAML config
  • Invalid YAML config
  • Missing YAML config

  I dont think this is necessarily blocking, especially since i think we might need some backend support crafting the tests.