Add new DAST schema fields to backend for API Fuzzing

What does this MR do?

1. Adding new security report fields to Vulnerabilities::Finding model.
2. Expose new fields through the vulnerability serializer

Issues with new fields:

• assets fields: #230242 (closed)
• add evidence.source fields: #230279 (closed)
• add body to evidence: #230092 (closed)
• add supporting_messages to evidence: #230132 (closed)

Related to #260432 (closed)

Screenshots

Manual test of vulnerability_findings with new fields marked in red:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] 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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team