Add support for CUSTOM_SERVER_PACK

[ronnierap]

If you have custom servers that require multiple files you can now specify them as a zip package (which will extract contents to the /data dir)

[itzg]

I seem to be missing docs for GENERIC_PACK, but your PR seems to be redundant with the intended combination of TYPE=CUSTOM and GENERIC_PACK where the custom server logic accounts for it here

docker-minecraft-server/start-deployCustom

Lines 23 to 25 in 28b7afd

	elif [[ ${GENERIC_PACK} ]]; then
	log "Using custom server jar from generic pack at ${CUSTOM_SERVER} ..."
	export SERVER=${CUSTOM_SERVER}

and then the generic pack is processed here

docker-minecraft-server/start-finalSetupModpack

Lines 154 to 186 in 28b7afd

	if [[ "${GENERIC_PACK}" ]]; then
	if isURL "${GENERIC_PACK}"; then
	log "Downloading generic pack ..."
	curl -fsSL -o /tmp/generic_pack.zip "${GENERIC_PACK}"
	GENERIC_PACK=/tmp/generic_pack.zip
	fi
	sum_file=/data/.generic_pack.sum
	if ! sha256sum -c ${sum_file} -s 2> /dev/null; then
	base_dir=/tmp/generic_pack_base
	mkdir -p ${base_dir}
	isDebugging && ls -l "${GENERIC_PACK}"
	unzip -q -d ${base_dir} "${GENERIC_PACK}"
	if [ -f /data/manifest.txt ]; then
	log "Manifest exists from older generic pack, cleaning up ..."
	while read f; do
	rm -rf "/data/${f}"
	done < /data/manifest.txt
	find /data/* -type d -exec rmdir --ignore-fail-on-non-empty {} +
	rm -f /data/manifest.txt
	fi
	log "Writing generic pack manifest ... "
	find ${base_dir} -type f -print0 | xargs -0 -I {} echo "{}" | sed "s#${base_dir}/##" > /data/manifest.txt
	log "Applying generic pack ..."
	IFS='
	'
	set -f
	for d in $(find ${base_dir} -type d); do mkdir -p "$(sed "s#${base_dir}#/data#" <<< $d)"; done
	for f in $(find ${base_dir} -type f); do cp -f "$f" "$(sed "s#${base_dir}#/data#" <<< $f)"; done
	rm -rf ${base_dir}
	sha256sum "${GENERIC_PACK}" > ${sum_file}
	fi
	fi