Remove runtime submodule

[TomasEkeli]

• removes the runtime git-submodule and puts the files directly under Source/content/en/docs instead of symlinking them from Source/repositories/Runtime
• removes the docsy git-submodule
  • removes the vendor submodules from docsy (bootstrap and Font-Awesome)
  • updates the refered mermaidjs to 10.2.3
• removes the github-action to update the runtime git-submodule (it no longer exists)
• removes the update-submodules step from netlify.toml
• updates the documentation-on-documentation to no longer refer to submodules
• adds an example-diagram to the writing-style -page

[TomasEkeli]

it's not REALLY 5000+ files changed. it's just that they appear in this repo now - not pulled in as submodules