Whitelisting rel properties #223

Is your feature request related to a problem? Please describe.

When sanitized, the rel property on links is completely replaced by the noopener noreferrer value, even though a correct value.

Describe the solution you'd like

Set a constant list of correct values that won't be replaced after sanitization. e.g.

const POSSIBLE_REL_VALUES = ["nofollow", "ugc", "sponsored", ...];

The list of possible values can be found here https://www.iana.org/assignments/link-relations/link-relations.xhtml

Describe alternatives you've considered

N/A