This MR adds new feature flag for DAST redesign

What does this MR do and why?

This MR resolves #360820 (closed)

New DAST profiler selection flow is being presented. Before this feature is stable it will work under this feature flag.

With FF enabled: new selection flow with side drawer is presented

With FF disabled: old selection and display process is presented.

How to set up and validate locally

1. Enable flag by enabling rails console in terminal

   Feature.enable(:dast_ui_redesign)

2. After testing, disable flag

   Feature.disable(:dast_ui_redesign)

This is initial MR for creating a feature flag.

Describe in detail what your merge request does and why.

MR acceptance checklist

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