Add hover highlights to CI config graph for needs jobs

What does this MR do?

This is part 3 of a series of MR to implement a graph preview of ci yaml configurations.

• Deliver the basic graph behind a feature flag without dependencies
• Deliver the job dependencies line between jobs
• Add hover on job pills that highlight all ancestors needs <-- You are here
• Add documentation
• Rollout feature flag

Behind a feature flag gitlab_ci_yml_preview

We now add interactivity where hovering on a job node will highlight all of the job it depends on

Below is a video of the behaviour.

Screenshots

Screen_Recording_2020-10-07_at_9.40.10_AM

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

Related to #241722 (closed)