Principle for treating configuration errors

This issue is about creating a policy, or principle, for treating wrong configuration.

There are two approaches: failure (raise an exception) or warn and continue operation if the nature of the configuration parameter permits this. Here: https://github.com/apache/incubator-druid/pull/7562#issuecomment-511452285 I proposed failure, but I'm ambivalent to whether this is right. Just warning also has an appeal, see "Define errors out of existence" idea [here](https://web.stanford.edu/~ouster/cgi-bin/cs190-spring15/lecture.php?topic=errorHandling) (or in a book "A Philosophy of Software Design"). So if somebody believes strongly in warning, I would support this policy.

The policy may be more detailed, prescribing failure or warning in different situations based on some criterion.

No file, test, or entry point is named in the issue. Start by reviewing the linked pull-request discussion and the referenced error-handling material, then establish agreed criteria for failing versus warning on invalid configuration; done means the project has a decided, documented policy.

Written by the indexing model from the issue text.