Ability to ignore "undeclared name" errors

### Description

I'm using `tfproviderlintx` with null-ls and so this means it is run on a file-by-file basis, rather than a project level. That means I see lots of "undeclared name" errors and I'd like to ignore them but I don't see an error code like I do with other errors.

For other codes I can name them as a flag, e.g. `"-XAT001=false"`