CKEditor5 Blog PoC

Summary

Closes #2333 (closed)

Depends on engine!448 (merged) This is a PoC for testing and evaluation.

We are going to need to fork the balloon editor and upload the package via NPM, so that we can make a lightly customized build where we enable the Alignment plugin. Because we are going the custom-build route, there is also no image upload, as the code for the UploadAdapter will likely change when separating from the Balloon build.

Steps to test

1. Make a new blog.
2. Edit it. The url should still be /blog/edit/:guid
3. Old editor should still work fine.
4. Change the URL to blog-v2 e.g. /blog-v2/edit/:guid
5. Play with new editor, remember alignment and upload are going to require additional work.
6. Save.
7. Hit edit again, it should link to the /blog-v2/edit/:guid again as the editor_version variable has changed

Estimated Regression Scope

As this is not to go live; there isn't a huge scope for regression. If this is tested on Staging or in another environment, any regressions would be in former blogs, as the v2-blogs route isn't known to users.