Add DAST on-demand scans site profile app

What does this MR do?

It bootstraps the Vue app that eventually contain the DAST profile library.

It is the first part of a series of MRs that will iteratively add more functionality. For now the App only contains a placeholder text for the profile-listing part and is hidden behind a feature flag.

Context

Related Issues / Epics

• Issue #229512 (closed)
• Epic &3786 (closed)

Local Tesing

In order to test this locally run the following command to enable the feature:

echo "Feature.enable(:security_on_demand_scans_feature_flag)" | spring rails c

1. Sign is as an admin user
2. Use an existing project's group / projectName for this url pattern /:group/:project/-/on_demand_scans/profiles (http://localhost:3000/h5bp/html5-boilerplate/-/on_demand_scans/profiles)

Screens

Desktop	Responsive Behaviour
	dast_profiles_library_responsive

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (not needed - behind auto-disabled feature flag
• [-] 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

Related to #229512 (closed)