[web] Add Editor Toolbar to markdown editor

[tbsbdr]

Description

User Stories

• As a user I want an editor toolbar for markdown files so that I can learn how to use markdown.

Value

• Simplicity and Ease of Use
• Portability and Compatibility
• Lightweight notetaking tool
• Flexibility in Conversion

Acceptance Criteria

• show markdown toolbar for markdown files (.md .markdown) ✅
• use syntax highlighting for code ✅
• default initial view can be configured per instance
• default Initial view ✅
  • favorite: blended Markdown/WYSIWYG view if possible
  • alternative: splitview
• ~WYSIWYG / Markdown toggle is available - needs to be discussed again useless ihmo 🟥 ~
• Editor toolbar gets shipped as standard feature ✅
• any other plaintext files (txt, css, yaml) don't show the toolbar ✅
• if the file is in read-onyl, render the file in viewer-mode
• toolbar-language can be set via preferred user language ✅
• theme can be set via user set theme ✅

cherry on top: show any plaintext file (.css, .yaml, .html ...) in corresponding syntax highlighting

Definition of ready

• Everybody needs to understand the value written in the user story
• Acceptance criteria have to be defined
• All dependencies of the user story need to be identified
• Feature should be seen from an end user perspective
• Story has to be estimated
• Story points need to be less than 20

Definition of done

• Functional requirements
  • Functionality described in the user story works
  • Acceptance criteria are fulfilled
• Quality
  • Code review happened
  • CI is green (that includes new and existing automated tests)
  • Critical code received unit tests by the developer
• Non-functional requirements
  • No sonar cloud issues

Visuals

blended Markdown/WYSIWYG view if possible

[AlexAndBear]

Additional lovely todos:

• Edit space description, should open markdown editor ✅
• kick marked and sanitizer, use toastui viewer ✅