[FEATURE] Implement Conditional policies in `.fossa.yml`

[evrardjp]

Important: Feature requests should be directed to support@fossa.com for faster response and prioritization. Requests may still be created here but they may not get immediate attention and may be closed in favor of internally tracked tickets.

Fine, I will do both. Support@fossa.com is not public.

Is your feature request related to a problem? Please describe.
I would like to define an exception that is not file/directory based for a license scan.
For example, my project has a general policy to not allow MPL, but under certain circumstances (vouched by legal) a specific dependency is allowed. I do not want to have my own fork of the policy, I want to use the conditional policy system to filter a certain dependency (like a go module) from my code or to pre-approve it.
https://docs.fossa.com/docs/configuring-conditional-policy-rules

Describe the solution you'd like
Ideally, extending the current schema to have the conditional policies described in code would be ideal.
It would allow me to define different set of rules in different branches.

Additional context
I do not know your architecture, and I do not know if the this is the right location. However, I do believe that the .fossa.yml per branch would be a great location to describe exclusions, as it would allow non-fossa admins to contribute on exclusions.

[github-actions]

Thank you @evrardjp for creating this issue. If this is in regards to a defect, product question or feature request: you should use our support portal at https://support.fossa.com to file a request, as you would receive more immediate support.