WIP: Resolve "Handle multiple sites in DAST reports"

What does this MR do?

The main goal of this MR is to handle multiple entries present in the DAST report (Refer #11930 (closed))

Additional changes:

• Update DAST report fixture to the latest format (#13034 (closed))
• During deduplication of occurrences, now also ignoring WASC identifiers, since they also represent a class (similar to CWE), so cannot be used for deduplication (As multiple occurrences can have the same identifier). Some vulnerabilities were getting deduplicated because of us not ignoring WASC.

Pending changes:

• Add fixture which has multiple entries in the report
• Add specs to handle legacy report
• Add specs to check logging/some error scenarios
• Verify UI

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #11930 (closed)