Visualization of .gitlab-ci.yml static file (MVC)

What does this MR do?

Adds a new section behind a feature flag gitlab_ci_yml_preview that lives in a tab when previewing your gitlab-ci.yml. For now, it is a simple graph that renders job in columns with a stage name at the top (see screenshots). This section only appears if the file is detected to be a gitlab-ci.yml file.

This MR is part of a 5 part effort to deliver an MVC:

• Deliver the basic graph behind a feature flag without dependencies <-- You are here
• Deliver the job dependencies line between jobs
• Add E2E tests to ensure that the feature is well hidden behind a feature flag and only appears on gitlab-ci.yml
• Turn on feature flag
• Support parallel jobs

Because this change is behind a disabled feature flag, it doesn't need a changelog.

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

Closes #241722 (closed)