Implement .repo file for RPM repositories

[pieterlexis]

Closes #5356
https://pulp.plan.io/issues/5356

Opened early for review, this needs tests and docs.

Basically, this PR makes the content server serve config.repo files at $CONTENT_PATH_PREFIX/rpm/$BASE_PATH/config.repo that look something like this:

[foo]
enabled=1
baseurl=http://localhost:24816/pulp/content/base_path
gpgcheck=0
gpgrepocheck=0

Or, when a metadata signing service is enabled:

[bar]
enabled=1
baseurl=http://localhost:24816/pulp/content/bar
gpgcheck=0
gpgrepocheck=1
gpgkey=http://localhost:24816/pulp/content/rpm/bar/public.key

Additionally, when the signing service is enabled, theres also a public key served at $CONTENT_PATH_PREFIX/rpm/$BASE_PATH/public.key.

@dkliban mentions in the issue:

the new handler should handle a route that looks like this: settings.RPM_CONTENT_PATH_PREFIX + '{path:.+}'. This is a slight variation on what pulpcore already provides[1].

However, the RPM repos did not have this prefix yet. Should the content for RPM always be prefixed with this or shall I remove it from this PR, pending a discussion on this?

[pulpbot]

Can one of the admins verify this patch?

[pulpbot]

Can one of the admins verify this patch?

[mdellweg]

Wouldn't it be easier to generate this file as part of a publication making it a PublishedArtifact instead of creating it on the fly in the content app?

EDIT: No, that's impossible (see https://pulp.plan.io/issues/5356#note-4)
Leaving the note here to prevent me from asking the same question again.

[dkliban]

@mdellweg Yes it would be, but then users would have regenerate a publication each time they want to use it with a new Distribution.

[pep8speaks]

Hello @pieterlexis! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-05-08 09:20:34 UTC

[bmbouter]

I read through the code and it all looks sane to me.

[dkliban]

Thank you! This is a great feature.