Support CHANGELOG.md file

[ghostdevv]

I think it would be incredible if a CHANGELOG.md file was automatically picked up and had it's own tab on the package page like the README does. It's quite common to see these files around! Happy to help with a PR if there is interest

[jollytoad]

Or if the changelog doesn't exist fallback to github release notes, or commit history ... I think this would fit in well with the whole concept of JSR minimising tooling required for publishing (as tooling is often used to build the changelog in the first place).

[lucacasonato]

I think having support for displaying a changelog in the UI would be great. My thinking:

• Only support CHANGELOG.md - start by parsing this file, assuming it is in the https://keepachangelog.com/ format.
• Render the changelog entries for each version into the versions on the Versions tab of each packages' page. That way we don't have to add another tab.
• In the future, it'd be really cool to be able to show "symbol diffs" between versions by comparing the generated docs. For example, if a new function is introduced in a release, we could surface this through the changelog.

If a user does not write a CHANGELOG.md manually, at least the symbol diffs can provide an overview of API changes (but not internals changes, like bug fixes).

[alexgleason]

I'm migrating to a Deno workspace and creating separate CHANGELOG.md files for each of my packages. Now I think it would be even more useful to display the changelog in the JSR UI.

I am using keepachangelog too, but the only thing I have to change is not linking them to git tag ranges anymore since I use different versions for different packages in the repo. So the git tag to release flow doesn't work anymore.