Update vulnerability_export API to accept report_data

Context

In a previous MR, we added a jsonb column to the vulnerability_exports. This field is used to store data assets from the frontend, to be used in report rendering.

This issue will introduce the first usage of the jsonb column. In this instance, we are going to store an SVG that has been computed in the frontend. Future usages may store json data blobs or some other data.

Implementation plan

• add report data as an API parameter
• update the vulnerability export API docs
• update the specs

References

• thread where we discuss the structure of the parameter's hash
• thread discussing the jsonb schema structure
• thread more discussion on the schema structure