Move pipelines CSS to page page_bundles

What does this MR do?

Related to #239861 (closed): Move pipelines CSS to page page_bundles

Pipelines CSS code is loaded in all pages, this change removes it and moves it to a page bundle file.

Note: This MR tries to avoid changing the CSS code, so we can handle merge conflicts easily. Other improvements to the CSS itself could be addressed in follow ups.

Screenshots

Related screens verified:

Pipeline Graph

Mini Pipeline

Commit	MR

Pipelines List

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