Allow append to Apache Rat exclusions

[grobmeier]

This patch should allow to append additional exclusions from the child parent

[grobmeier]

Usecase: Chainsaw contains *.log files for testing purposes, they cannot have a license. I am not sure if adding *.log is a good idea to the rat config, but maybe it is

[vy]

@grobmeier, since this is only a Chainsaw-specific problem, why don't we only add a **/*.log exclude there? For instance, Log4j has several such RAT overrides.

[grobmeier]

Because it didn't work yesterday - I might have done something wrong. After further clean up, the combine.children="append" property works as expected, so this PR with using combine.children="append" might not be necessary. I assume it could serve as a default though. but not necessary

[grobmeier]

Btw, log4j2 also excludes log files:
https://github.com/apache/logging-log4j2/blob/2.x/pom.xml#L558

[vy]

@grobmeier, I am not a big fan of "can be useful" ideas. If it helps with something, let's do it. Otherwise, let's wait until there is a use case. But that is me, and this is an innocent change. I leave it up to you. You can either merge or close the PR. Both are fine by me.

[grobmeier]

The use case is that almost every use has specialties that needs to be appended, so it makes sense to me to define append in the parent and not in all childs. Is this use case strong enough for you.

[vy]

Sounds good, merging.