Added docs from the pulp-2.4 branch.

This commit adds in the documentation changes that were present in the
pulp-2.4 branch that were not present in the 2.4-release branch. This
commit was generated using this command:

$ git diff 2.4-release..pulp-2.4 docs/
Merge branch '2.4-release' into 2.4-testing

Conflicts:
	docs/sphinx/user-guide/release-notes/2.4.x.rst