WIP: EE: pipeline graph durations

What does this MR do?

A start towards https://gitlab.com/gitlab-org/gitlab-ee/issues/2666.

Shows durations for each stage and group in the pipeline graph. Could be useful for developers looking to identify which are the slowest jobs in their pipeline

Currently triggered by appending ?timings=1 to the pipeline show URL. Eg. /pipelines/82?timings=1. I plan to put this behind a per project feature flag as well.

The UX might be bit crude currently but I think it will be valuable for &25

Screenshots

TODO

• Specs
• Query performance
• License project policy
• CE MR / EE specific things
• Docs
• Put behind Feature Flag

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

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