Use json path to define adjustments within the upgrade steps

AT:

• all upgrade steps use json path, if possible, to define which field they want to modify instead of defining a complex mapping
• all step operations can still be performed

Context:
Define a mapping provides the developer with a lot of power, but makes it really hard to write/understand an upgrade step. Also we should avoid to write json in java as much as possible, since it's hard to read and a pain in the a**.