Add maven.config to .gitignore

This allows to use it comfortable to configure personal preferences for running maven.
One example is to disable build caches.

Original pull request #2039

Author: schauder

.gitignore

@@ -11,6 +11,7 @@ target/
 *.graphml
 package-lock.json
 .mvn/.develocity
+.mvn/maven.config
 
 build/
 node_modules