New Empty state for DAST Profile Selectors

What does this MR do and why?

This MR partially resolves #355640 (closed). This MR creates new empty state for scanner profile selector and site profile selector, according to new design.

1. New empty state is currently behind :dast_ui_redesign feature flag.
2. Two new components for scanner and site profile empty state are presented in this MR.
3. After finishing redesign of summary card, empty state can become of profile_selector
4. Right now it is extracted to own component and conditionally shown in parent component, in order to make it work before summary redesign is finished.
5. It is also extracted in two components and not implemented with only one with slots, in order to improve code readability. As on_demand_scans_form.vue is already big and complex enough.

Describe in detail what your merge request does and why.

Screenshots or screen recordings

before

after

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How to set up and validate locally

1. Enable feature flag

   Feature.enable(:dast_ui_redesign)

2. Go to any project /root/$PROJECT_ID/
3. Go to /root/$PROJECT_ID/-/on_demand_scans/
4. Go to new scan form by clicking new scan

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.