Respect setting of M2_HOME or MAVEN_OPTS

[imagejan]

jgo (at least when launched via Python: python -m jgo) currently doesn't respect when the environment variables M2_HOME or MAVEN_OPTS are set.

We currently default to this:

jgo/src/jgo/jgo.py

Lines 430 to 434 in 89d20d1

	config.set(
	"settings",
	"m2Repo",
	os.path.join(str(pathlib.Path.home()), ".m2", "repository"),
	)

Maybe we can do something similar to handling the JGO_CACHE_DIR variable?

jgo/src/jgo/jgo.py

Lines 726 to 729 in 89d20d1

	if os.getenv(jgo_cache_dir_environment_variable()) is not None:
	cache_dir = os.getenv(jgo_cache_dir_environment_variable())
	_logger.debug("Setting cache dir from environment: %s", cache_dir)
	config.set("settings", "cacheDir", cache_dir)

Related: #57.