feat: Add .editorconfig, .gitignore, and .vscode/extensions.json files

[MicLieg]

This PR adds multiple VSCode extensions to help developers write more consistent Markdown:

1. editorconfig
   • Override user/workspace settings with settings found in .editorconfig files
2. markdown-all-in-one
   • (Almost) All you need to write Markdown (keyboard shortcuts, table of contents, auto preview and more)
3. vscode-markdownlint
   • Markdown linting and style checking for Visual Studio Code
4. prettier-vscode
   • Code formatter

It also adds the required .editorconfig file.

Related Pull Requests:

• https://github.com/GameServerManagers/LinuxGSM/pull/4527
• https://github.com/GameServerManagers/LinuxGSM-Dev-Docs/pull/8