Add DAST Saved Scans tab

What does this MR do?

This addresses issues #295246 (closed) and #295245 (closed) by:

• Adding a new Saved Scans tab to the DAST profiles management page. This new tab is only available when the dast_saved_scans feature flag is enabled.
• Mocking the dastScans GraphQL query to demonstrate how the new tab will behave. The actual query will be implemented as part of #295248 (closed), where the mocks will be removed as well.
• Updating a few copies to better reflect the fact that we're managing more than DAST scanner/site profiles from this page now.

How to test this?

1. Enable the :dast_saved_scans feature flag.

echo "Feature.disable(:dast_saved_scans)" | rails c

2. Navigate to the DAST scans management page at /:namespace/:project/-/security/configuration/dast_profiles

Screenshots (strongly suggested)

Before	After

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (feature flag)
• [-] Documentation (if required) (#295618 (closed))
• 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

Related to #295246 (closed) & #295245 (closed)