[Feature] Show link to changelogs in update PRs

[dreua]

It would be nice to have a link to each package's changelog in the PRs. For some dependencies I'd like to review them before merging. At least for Pypi I assume a changelog link should be easy enough to get via the API, other platforms could be added on demand.

What do you think about that idea?

[dreua]

Any thoughts? Would you merge if I implemented it myself?

[wjt]

Sounds great to me!

[dreua]

I've added two PRs which already work for me locally. Feedback welcome!

First I thought that the changelog link would need to be a template (to insert the current version) but in my limited test so far I ended up with static urls only, so the name changelog-url-template is currently not adequate. Either there should be actual templating support or the name needs to be changed. Shorter might be better anyway, but I'd love to get some feedback before I start changing it.

Example manifest, the submodule already contains autogenerated test data by the pip generator.

[dreua]

I think I'll just rename the keys to changelog-url without template. Templating support can still be added later if needed, but for now I don't see the need. Any other feedback or ideas? (@wjt, @stsdc)