Breakdown `pipeline_editor_app` into smaller components

Summary

app/assets/javascripts/pipeline_editor/pipeline_editor_app.vue is a pretty big component already. It would be beneficial to break it down into smaller component and even offset some of it's logic to them when it only concerns the content of one of the tab. The pipeline_editor responsibility should simply be to fetch the data and create the top-most structure of the page

Improvements

• Easier to test
• Separation of concerns
• More readable

Risks

As in any refactoring, this could break the code.

Involved components

app/assets/javascripts/pipeline_editor/pipeline_editor_app.vue spec/frontend/pipeline_editor/pipeline_editor_app_spec.js