Provide pulp_rpm urlencode solution to plugins via the plugin API

Is your feature request related to a problem? Please describe.
pulp_deb users have reported the following issue: https://github.com/pulp/pulp_deb/issues/571
It looks like pulp_rpm has solved the exact same issue for pulp_rpm a long time ago here under this issue.

Describe the solution you'd like
Since this now affects multiple plugins, it would be nice if the pulp_rpm solution could be provided to plugins by pulpcore.
Ideally using the downloader from pulpcore would "just work" for everyone, but given the ongoing design discussions around downloaders and the pulp_rpm solution describing itself as "a pretty ugly workaround" perhaps just provide it as a small utility function requiring opt-in from plugin authors?

Describe alternatives you've considered
We simply copy the pulp_rpm fix within pulp_deb and maybe wait for the "Pulp downloader redesign" to conclude before asking for a general solution from pulpcore.

Start by comparing the existing workaround in pulp_rpm/app/downloaders.py with pulpcore's downloader and the plugin API. Review the linked downloader redesign discussion before deciding how an opt-in utility should be exposed; done means multiple plugins can use the shared urlencode behavior without copying the workaround.