Github workflows for Mac, Linux, and Windows installers

[shannah]

Created a fork and added a github workflow to generate Mac, Linux, and Windows installers, with auto-update using jDeploy.

https://github.com/shannah/Pixelitor/releases/tag/4.3.1

It auto-generates these on release, and also generates installers which are bound to the master branch.
https://github.com/shannah/Pixelitor/releases/tag/master

I can create a PR if this is something that you'd like.

[lbalazscs]

Thank you for your effort, jdeploy is very impressive, but (at least at the moment) I don't think that it's what I need for Pixelitor. I mainly plan to use jpackage or maybe graalvm-based installers.

BTW, I found a small error on the page https://www.jdeploy.com/docs/manual/
It says "Java versions from 8 through 17 are supported", but obviously Java 21 (required by Pixelitor) is also supported.

[shannah]

Thanks. Those things are the hardest part of docs to keep up to date. In theory it should continue to work with every new version of java, but you don't know for sure until they are released.

I'll continue using these installers until you get the jpackage ones up and running.

Keep up the great work on this app. Outside of IntelliJ, it is the most polished Swing app i've run across in the wild.