Prettier issues with Vue templates

Summary

This issue tracks problems and gotchas (and possibly workarounds) for Prettier causing problems with Vue templates.

Known Issues

• Prettier needs singular tags (<br>, <img>, <input>, etc) not to have closing / while ESLint insists on having those.
• Certain template structures may cause addition new line characters leading to weird alignment issues (eg; see https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8431#note_122522591).