URLs in body for projects are relative in the Mock plugin and creates 404s links and broken images

Problem/Motivation

After reviewing #3292996: Create a skeleton for the individual module page, we found out that the body contains many relative URLs which the D7 www.drupal.org does not transform when serving the data, so we should take care of this within the plugin.

I think that a good place to do this would be the "getProjects" method inside the Mock plugin. In there, we massage the data to be in the right format, so we take what the api gives us, and tweak it to what project_browser needs (ie: we transform taxonomy_vocabulary_46 into field_development_status). So I think that'd be a good place to put something like this:

$project['body'] = $this->relativeToAbsoluteLinks($project['body'], 'https://www.drupal.org');

Which would take the body and a base URL and then prepend that to any part of the $project['body']['value'] that contains a relative URL. See the answer to this question in stackoverflow as reference: https://stackoverflow.com/questions/48836281/replace-all-relative-urls-w...

This could be filed as a separate issue altogether, but I think that shipping a page that looks like the below would look weird:

Steps to reproduce

See the above image when testing the parent issue.

Proposed resolution

Convert relative URLs to absolute.

Remaining tasks

• ✅ File an issue about this project
• ☐ Manual Testing
• ☐ Code Review
• ☐ Accessibility Review
• ☐ Automated tests needed/written?