Add bare minimum Modrinth configuration

[bloxgate]

Adds a gradle task that will publish if you have your MODRINTH_TOKEN set. Still manual at the moment

At the moment running this would create a version identical to the current 1.0.1 version, including the changelog.

ToDo:

• [ ] Automate this to publish on some criteria

[jrddunbr]

Recent merges mean that this PR needs to be rebased/refactored a bit.