Make Warning the default setting for internal trace logging

[CharliePoole]

Historically, the console runner has used "Off" as the default for internal trace logging.

An argument can be made that "Error" or even "Warning" is a better choice and that turning all logging off should require a user decision.

@nunit/engine-team @nunit/core-team What do you think?

[stevenaw]

A default level of Warning makes sense to me as anything at that level or higher may require scrutiny to ensure everything is as it should be.

Logging could then be made more verbose for situations or users who require it, or even off based on preferences.

[veleek]

We have warning as our default log level for many of our services so having the same for test libraries seems totally reasonable.

[CharliePoole]

I'll go with Warning then.