This PR tries to enhance the overall maintainability of rumqtt.
Note that this PR is not ready to be merged because the code style (clippy) must be applied to the code.
What has been changed:

• Stale (bot) is a GitHub action
• Better CI/CD with enhanced checks and automation
• VSCode compatibility
• All files must respect a format/coding standard for better consistency (e.g. .rs has fmt/clippy, .sh has prettier/shellcheck, etc...)
• Added EditorConfig
• Markdown linter via markdownlint
• Prettier file formatter
• Code spell checker via cspell. A lot of typos have been found and fixed
• rumqttd Docker image is now based on gcr.io/distroless/cc (from Google) to enhance overall security since "it does not contain package managers, shells or any other programs you would expect to find in a standard Linux distribution"
• Multi-manifest Docker image using Docker buildx. The new Docker image is arm64 (aarch64) and amd64 (x86_64)
• More robust and fully configurable scripts (see scripts directory). Also POSIX compliant
• rumqttverifier sources are now based on Typescript for better maintainability and more. Simply run npx ts-node path/to/script.ts instead of old node path/to/script.js
• Cross compilation:
  • aarch64-unknown-linux-gnu -> rumqttd-1.0.0-aarch64-unknown-linux-gnu
  • aarch64-unknown-linux-musl -> rumqttd-1.0.0-aarch64-unknown-linux-musl
  • x86_64-unknown-linux-gnu -> rumqttd-1.0.0-x86_64-unknown-linux-gnu
  • x86_64-unknown-linux-musl -> rumqttd-1.0.0-x86_64-unknown-linux-musl
    I need to test Cross a little bit more but it seems to work without any problem. We could add Windows!
• Updated release profile

  [profile.release]
  codegen-units = 1 # Better optimization
  lto = true # Link time optimization
  strip = true # Stripping

• Minimum supported Rust version. I've set it to 1.64.0 due to Cross requirement but it can be changed to better suit your needs
• Rust edition is set to 2021
• Much more...

Please, let me know what you think and what you want to change/update/add/delete 🥳

PS: Thanks for developing rumqtt*