Support other linux service managers

[reubenmiller]

Add support for additional linux service managers in addition to systemd.

Overview

• Ideally a system's service manager should be automatically detected at install time, and the appropriate one selected
• Add support for the following service managers
  • openrc (used by Alpine Linux)
  • SysVinit (used by Yocto)
  • s6-overlay (docker friendly service manager)
  • runit
  • supervisord (python based service manager)
  • ~Upstart (used by older WSL/WSL2 installations)~

[reubenmiller]

Service managers are now supported via optional packages. Below contains the relevant information about where to find information about the source files and how to use it:

• New optional install script to install the relevant service manager (based on auto detection). Instructions have been updated in the docs: https://thin-edge.github.io/thin-edge.io/next/install/#optional-linux-distributions-without-systemd
• Packages are hosted in the community cloudsmith repository: https://cloudsmith.io/~thinedge/repos/community/packages/
• Service definitions are hosted in a separate repository: https://github.com/thin-edge/tedge-services