Third Party Flows in the Ai Catalog

We need to add the ability to add new Third party flows in the AI Catalog with a type field and a yaml editor. For the MVC, we can start without any custom schema and focus solely on having a YAML editor for the configuration re-using the source editor component https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/vue_shared/components/source_editor.vue

An example implementation can be seen in the pipeline editor component, which is also a yaml only editor https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/ci/pipeline_editor/components/editor/text_editor.vue

• The new type field will just be the existing item_type with a value of third_party_agent
• The definition json should match this yaml file in a private project. We basically need a commands and variables array, a injectGatewayToken boolean and a string for the image.
• We will have all the same attributes for name, description, public, released, versions etc. as we do for other catalog items.
• The code base currently refers to everything as third_party_agent, though this seems to align more closely with what we'd consider flows.