md-editor-v3 Major version bump

[kulmann]

Initial Checklist

• I understand this is a user story and questions should be posted in the Community Discussions
• I searched issues and couldn’t find anything (or linked relevant results below)

User Story

As a web team member, I want to use the latest major version of md-editor-v3 so that I can remove a hack for collapsing long links in the ui.

User Value

• Up-to-date dependencies
• Less hacks in the code base

Acceptance Criteria

• md-editor-v3 is updated to major version 6
• no regressions in our integration:
  • long links still collapsed (that's in fact one of the new features of the lib)
  • preview-mode still renders markdown pretty
  • image uploads as blob still work