Splitting kvp on '=' creates bug if the string contains more than one '='

I have a string that's being parsed that looks like this "JAVA_OPTS=foo=bar&&baz=buzz". When the string is split at src/pycomposefile/compose_element/compose_list_or_map.py, line 18, an error occurs due to the split assuming exactly one '='. Recommend splitting on the first instance of '=' so the value in the kvp can contain one or more '='.