[FR] add relation reference type support

[pgsfredda]

Hi.

No slug is generated for the relation fields.

Currently the plugin produces an object-object slug label for those types of fields.

Strapi: 4.11.4
Strapi Plugin Slugify: 2.3.3
MySQL: 8.0.30 (MySQL Community Server - GPL)

[daedalus]

Thanks for the request, see my reply in #101 (comment)

[Ray Hughes]

+1 for relationship support