Default to CONTAINERBASE_TOOL_VERSION instead of TOOL_VERSION

[rarkins]

i.e. we should support and primarily document args like CONTAINERBASE_YARN_VERSION and not YARN_VERSION

[rarkins]

I'm guessing it's here:

base/src/usr/local/containerbase/utils/version.sh

Lines 37 to 43 in 4c6283d

	function get_tool_version_env () {
	local tool=${1//-/_}
	check tool true
	tool=${tool^^}_VERSION
	echo "${tool}"
	}

[rarkins]

Related: #101 (comment)

[viceice]

I'll prefer CONTAINERBASE_<tool>_VERSION in favor of <tool>_VERSION but will leave a fallback to <tool>_VERSION for a while.
so we can migrate all our repos step by step

maybe log a warning when old env is used? so it's deprecated. and support will be removed in a later version.