DAST On-Demand Scans - Use existing site profiles for scans - Frontend

• Related issues: #230612 (closed), #232487 (closed), #233371 (closed)

What does this MR do?

This adds support for using existing DAST site profiles when running a DAST On-demand Scan.

How to test this?

• Enable both feature flags.

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

• Visit a project's on-demand scan form: /:group/:project/-/on_demand_scans/.

Screenshots

Description	Screenshot
Site profiles could not be fetched
Site profiles loaded successfully
Site profile selected
No site profiles created yet

Recordings

Description	Recording
An unknown error prevented the DAST site profiles from loading. In this case we don't show the form at all as it would't be functional without the profiles.	Screen_Recording_2020-08-04_at_4.53.35_PM
Site profiles are fetched successfully, we can show the form.	success
When selecting a site profile, its summary appears below the dropdown.	site_profile_selected
User didn't create any DAST site profile yet, we show a button to create one.	no_site_profiles

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (not needed, this is behind a 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