POC Changelog viewer

[Sarabadu]

Summary

The upgrade helper really makes the most common changes easier to be highlighted, but for the changes that are not in the create-app we have 2 cases:

• If the package lives in backstage/backstage repo the cli will point out to the changelog file for that package :noice:
• If the package lives somewhere else, the cli only warns you about posible changes.

In this POC we are adding a new route that gets the package name and version as part of the url and queries the changelog file for that package and version from npm (just CHANGELOG.md for now, maybe requires more posible names in the future.

NOTE: this POC was made on top of this big PR #20 , and It requires some work to make it mergable recommend to look on 5d7b427 commit for the POC part

How it looks

You can see it working here https://sarabadu.github.io/upgrade-helper/changelog/@backstage-community/plugin-announcements/0.1.2 , changing the packages and versions

Thoughts

• The npm api used here in not documented, so it could get some silent braking changes
• The changelog content is queried from the package version it self, so in contrast with showing the github file on main this will show only the relevant changes for the updated version and not include any next version changes

Test Plan

What are the steps to reproduce?

Checklist

• I tested this thoroughly
• I added the documentation in README.md (if needed)