localsettings.properties is Parasoft own format containing set of predefined key-value pairings, which enable configuring your local environment, setting up reporting options, task assignments, licensing details and more.
You can find a list of keys and values which can be recognized by the tool in Parasoft Jtest User's Guide.
Generally those options are supposed to be stored in a separate file either locally or on your Concerto server (more information here).
Still, if you'd like to extend list of options imported from Concerto in your pom.xml file, you can do it by explicitly entering key-value pairings, preceeded by additionalProprties tag decribed here.
Please also take a note that there's not much you can do with Parasoft Jtest Maven plugin without having a licensed copy of the software itself set up locally or remotely (more information here).