Adds an overview stage to VSA

What does this MR do?

Adds the overview stage to the VSA path navigation. This only applies when the value_stream_analytics_path_navigation feature flag is enabled for VSA, on the overview stage only VSA metrics and charts should appear, any other stage should only display the stage table.

When the feature flag is disabled, the overview stage should not appear, the charts and stage table shold also appear on all stages.

This MR:

• When the overview is selected, we should display metrics and charts
• Other selected stages should only show the stage table
• Adds the home icon for the overview stage
• updates related specs to reflect the different behaviour when the hasPathNavigation feature flag is enabled / disabled

Related to #321438 (closed)

Screenshots (strongly suggested)

Feature flag on - overview	Feature flag on - other stage	Feature flag off

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
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• 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

Related to #321438 (closed)