Circle of update is a spiral

New

• Added a sponsoring button to the repository, as some nice people
  want to show their appreciation this way.
• Added GitHub Action to automatically deploy new releases to Docker Hub.

Changed

• Update to newest version of Wildduck, ZoneMTA, Haraka and Wildduck's
  Haraka-Plugin. Configuration has changed, make sure to update configuration
  files accordingly.
• Update node to v14 as Wildduck makes use of optional chaining now.