Allow configuration of config.properties

[okafke]

While the action appends to the config.properties, for some keys it's not possible to provide an own configuration, as they are going to appear twice in the config.properties. Perhaps, for these keys we should check their existence in the config.properties first.

mc-runtime-test/action.yml

Lines 52 to 62 in f170c7a

	- name: Bootstrap HeadlessMC
	run: |
	mkdir -p HeadlessMC run/mods
	cat <<EOF >> HeadlessMC/config.properties
	hmc.java.versions=$JAVA_HOME/bin/java
	hmc.gamedir=$PWD/run
	hmc.offline=true
	hmc.rethrow.launch.exceptions=true
	hmc.exit.on.failed.command=true
	EOF
	shell: bash