Add an option on finding to determine whether it is internal or external

[Camille-Arsac]

Is your feature request related to a problem? Please describe
In Defect Dojo, you can't just put the origin on a product, when this information is also needed for finding.

Describe the solution you'd like
There should be a field in the findings to indicate whether it's an internal or external publisher. By default, the option is set to internal, but if the finding is external, we need to be able to modify it to be able to follow the finding (i.e. without going through risk acceptance).

Describe alternatives you've considered
You can use tags, but as there are no restrictions on this field, it's too permissive.

Additional context
N/A