[PULP-276] Add support for prns

[pedro-psb]

Notes:

• The copy API used to check if objects belonged to the current domain. For PRN references, we'll have to do it in the task context to avoid response timeouts.

[pedro-psb]

This was copied from the PR adding PRN to pulpcore: pulp/pulpcore#5813.
It did catch the DistributionTree case, where it did not had prn specified.

[pedro-psb]

I've ran a few experiments after on-demand syncing >10,000 package from centos and here are some conclusions:

1. The distinct query suggested by @dralley is better! [0]
2. The extract_pk performs very poorly with pulp_hrefs because of the use of django's resolve. [1]

[0] Query comparision w/ list of 10,000 packages prns

In [54]: timeit(lambda: Content.objects.filter(pk__in=(extract_pk(n) for n in prns)).values("pulp_domain").distinct(), number=10)
Out[55]: 0.17054506699787453

In [56]: timeit(lambda: Content.objects.filter(pk__in=(extract_pk(n) for n in prns),pulp_domain=domain).count(), number=10)
Out[57]: 0.6148349700015387

[1] Very bad performance with extract_pk from pulp_href

In [34]: timeit(lambda: [extract_pk(n) for n in prns], number=10)
Out[34]: 0.023607832001289353

In [35]: timeit(lambda: [extract_pk(n) for n in hrefs], number=10)
Out[35]: 22.53728126399801

In [36]: len(prns)
Out[36]: 10000

In [37]: len(hrefs)
Out[37]: 10000

[dralley]

Great!

If we can do all validation in the view layer with clever queries, that would be greatly preferable to deferring it to the task.

If we can reimplement extract_pk such that it doesn't use Django's resolve(), but still do the validation we want to do, that would be ideal.

[pedro-psb]

This is ready to review, but I'm not sure how to handle lowerbounds incompatibility.
I'm expecting that when we declare compatibility with pulpcore 3.70 our requirements will be >=3.70, <3.85.
If not, some conditionals will be required to handle it.

[dralley]

Content to be copied into the given destinations from the given sources.

[dralley]

Remove the TODO

[dralley]

At the very least this function should have a comment stating that it shouldn't be used on anything but RpmRepository and RepositoryVersion types. But it would also be good to throw a ValueError if it's not one of those types.

[dralley]

Approved apart from the last request