Fetch and display plugin versions from repo

[daun]

Description

• Fetch current package version from the repo's package.json
• Display the package version next to the repo button, and link directly to repo's CHANGELOG.md
• Abstract repo file fetching into new function loadGitHubRepoFile
• This should work since all merges to master in plugin repos trigger a docs rebuild

Screenshot

Checks

• [x] The PR is submitted to the master branch
• [x] The code was linted before pushing (npm run lint)
• [x] All tests are passing (npm run test)

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[hirasso]

Nice. I'd prefer one button that would lead to the repo's main page. But the word "Repo" could be replaced with the version number. The GitHub logo on the button communicates it clear enough that it's a link to GitHub IMO.

If you insist on the the two button solution, there needs to be done a little bit more optimization for mobile devices:

[daun]

I liked having a way to link to the changelog directly, to make it easier to update sites with many plugins. But I get the point of using a single button. Let's do that. Maybe we can tack on the changelog at the end, in a collapsible details tag?

[hirasso]

Sure, a link to the changelog at the bottom sounds fine to me