Ability to "hide" a config from the __str__ so as to mask passwords or credentials when logging/printing the config

[bzadon]

Much similar to "omegaconf_ignore" Annotated metadata on config member variables, it would be great to have a metadata setting to omit the said config member variable from str or other "print" methods. This would allow using omegaconf for passwords or other authentication credentials without worry they would "leak" into log files.

TY!