Shorten the format of properties


Today its format is
 Properties":[{"name":"some_key","value":"some_value"}]

Since "name" and "value" are erroneous the format can be shorten to
 Properties":[{"some_key":"some_value"}]

This pull request is based ontop of https://github.com/majikthys/log4j2-logstash-jsonevent-layout/pull/7
 (it needs be merged afterwards, and only commit https://github.com/finn-no/log4j2-logstash-jsonevent-layout/commit/800fa8e931fb6d42507995915578b60a2189c433 needs be evaluated)