Add a config to disable the u-case safe features

[serradura]

To avoid a fragmented codebase where some exceptions are handled with rescue and on_exception hook. The idea is to create a feature toggle which will forbid the usage of Micro::Case::Safe, Micro::Cases::safe_flow() and Micro::Case::Result#on_exception to ensure that will have only one way to handle exceptions, in that case, using a standard rescue statement.

Thanks, @lunks for helping me to elaborate on this idea.