Add "Scan library" tab

What does this MR do and why?

This adds the Scan library tab to the on-demand scans index page. It lists all saved DAST profiles with a link to edit them. In the next MR, we'll add more actions as per the designs.

Screenshots or screen recordings

How to set up and validate locally

1. Navigate to the on-demand scans index page at Security & Compliance > On-demand scans.
2. Activate the Scan library tab.
3. If you have created at least one DAST profile, it should show up here. Otherwise, create one by clicking on New DAST scan in the top right corner.

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 #341379 (closed)