Allow users to supply distribution and component when modifying repo contents

[daviddavis]

Today, when you upload a package into a repo, you can specify what distribution or component you want it to land in and pulp_deb will create the necessary components for you like PackageReleaseComponent. No such feature exists though for the repository modify endpoint. I imagine could add these parameters though (distribution and component) to the endpoint and have similar functionality.

[quba42]

Ideally users don't ever need to manually manage PackageReleaseComponents and company (at least not for standard workflows).
This is very much a step in that direction.

I am very much playing with the thought of making this a breaking change down the line, by either making the new parameters required, or else by making them default to some default value if not supplied...