Add automated test for "Grant Like right from Extension Rights"

The manual test is here: https://test.xwiki.org/xwiki/bin/view/Security%20Tests/Grant%20Like%20right%20from%20Extension%20Rights

The test verifies whether or not granting a Like right to an user from Administer Wiki > Users & Rights > Extension Rights is working properly.

The Extension Rights was introduced in XWiki 13.5 and according to the discussion, at this moment there are no automated tests for it yet.