`content-property-no-static-value`: Add exceptions for quote values

[tetarchus]

The content property allows for special keyword values for display quotation marks.

content: open-quote;
content: close-quote;
content: no-open-quote;
content: no-close-quote;

This rule currently highlights these as incorrect from an accessibility POV as it thinks it's static text content.

Is it possible to add an exception for these values which are purely presentational and wouldn't impact accessibility users? Likely as an option (default 'false' to maintain existing functionality) to the rule to allow users more control over whether these are allowed.