extending #[redact(with = 'X')] to support Strings

[nick-schafhauser]

currently the #[redact(with = 'X')] attribute is limited in that you can only specify one single character that the string will be redacted with.

What do we think about enhancing this attribute so that it can support Strings instead of just chars?

Here is an example of what I am proposing:

#[derive(Redact)]
struct Foo {
    #[redact(with = "[REDACTED]")]
    redact_me: String,
}

fn main() {
    println!(
        "{:#?}",
        Foo {
            redact_me: "Super Secret String".to_string(),
        }
    );
}

// Running main would print the following:
Foo {
    redact_me: "[REDACTED]",
}

Now I am not sure how this would play nicely with the partial or fixed attributes, so perhaps reusing the with attribute to support a String or Char isn't the way to go.
One thought I had was to add another attribute, perhaps #[redact(with_string = "[REDACTED]")] that would be mutually exclusive with partial or fixed

Would love to hear what others think about this sort of thing