Refactor pipeline form to Vue

What does this MR do?

In our product space coming up we have some feature requests for pipelines/new. This feature is in HAML and will be difficult to ship the features that are requested. And will not be that great to maintain. This MR is moving the feature over to Vue behind a feature flag new_pipeline_form.

The UX interactions have stayed the same, but we are now using our component library.

Some of the UX changes I made:

• The icon was changed over to issue-close (the closest I could find within our SVG library).
• The value field was changed from textarea to input. We have some CSS overwriting any util classes if we want to set a height on the textarea.
• We are using gitlab-ui now. yay!

The goal of this MR is to move this feature to Vue with all existing functionality working as expected.

Video

pipeline-new-form

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team