Add alert message to pre-scan verification sidebar

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR resolves #378272 (closed)

This MR adds alert message on top of sidebar.

Alert message has different states.

backend is still in progress, so this MR covers only frontend part for now

Task/issue	MR
Create feature flag / lay groundwork - #376687 (closed)	!100322 (merged)
Create pre-scan verification component - #376690 (closed)	!100593 (merged)
Add drawer for pre-scan verification - #376708 (closed)	!100694 (merged)
Add status summary component to a drawer - #377509 (closed)	!100937 (merged)
Add stepped list for pre-scan verification flow - #377854 (closed)	!101257 (merged)
Add alert message to a sidebar - #378272 (closed)	!102389 (merged)
Add option on Scan Library page - #376705 (closed)	!102290 (merged)
Add Pre-scan verification column to Scan Library tab - #376692	TBD

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

close_alert

How to set up and validate locally

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

1. Enable flag by enabling rails console in terminal

   Feature.enable(:dast_pre_scan_verification)

2. Edit the code to force the alert to show (instructions here)
3. Go to BASE_URL/PROJECT_ID/-/on_demand_scans/new
4. Scroll down to a bottom of form you should see new component before submit button click on verify configuration
5. Or go to {URL}/{PROJECT_ID}/-/security/configuration/dast

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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

Related to #378272 (closed)