feat: Add CSAF file generator

[anthonyharrison]

The CSAF V2.0 spectification is now finalised and provides a standard way of sharing vulnearability information.

Initial release is to generate a CSAF file in JSON format using the reported vulnerability information.

[Arnavk194]

@terriko I think this issue can be closed for good, already been handled by GSOC project 2024.

[terriko]

Thanks @Arnavk194 -- I'll get it closed now.