feat: Update relative links in docstrings of objects from other packages

[pawamoy]

Is your feature request related to a problem? Please describe.
Sometimes we render objects from other packages, or objects inherited from classes from other packages. If these objects contain relative links, these links should be fixed to be absolute instead, since they refer to parts of their own docs, not of ours, and would lead to 404s, or sometimes incorrect parts (same page URL/name, missing fragment, etc.).

Similarly, autorefs links should be fixed too, depending on their originating package. For example, autorefs links in a docstring of an object coming from copier should be made absolute using Copier's docs URL, not relative to our own. Without that, duplicate autorefs ids across docstrings from different packages would clash and lead to incorrect results.

Describe the solution you'd like
Relative (autorefs) links should be made absolute if coming from other packages.

Describe alternatives you've considered
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Additional context
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