Scope css pipeline graph rules to the pipelines show page

What does this MR do?

Part of #239861 (closed)

Scope css rules to the pipelines show page

Scope pipeline graph CSS rules to a single page via a selector for the page: projects:pipelines:show, so they can be later moved to an individual pipeline page (projects:pipelines:show).

The following selectors have moved:

• .pipeline-tab-content Pipelines tab in the page.
• .pipeline-graph Pipelines full graph view
• .dropdown-counter-badge Used in parallel jobs.

This change helps scope them only to that page while the rules are moved.

Screenshots

Related view if a simple pipeline, no changes are expected:

When the pipeline has upstream/downstream pipelines

For parallel jobs:

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

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• 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