Preprocessors for ObjectMapper before deserializing field

[Rothes]

A preprocessor modifies the node created by nodeResolver, before doing the deserialization.

This can be used to relocate old node key to this one, when node path is changed due to config schema change, with annotation like @RenamedNode(String oldPath).

For tiny schema change, this way could be much easier to do configration migration.

This cannot be done with current API, unless implement own nodeResover.

If possible, I could create a PR for this.