Support gitmoji commits

Thanks for creating this great action! I would like to use is with gitmoji based commits like 📝(README): Updated README with info, but it seems not possible with the current separators. As the above example, which refers to the docs: conventional commits type, can also be represented by :memo:(README): Updated README with info, I thought I can just add them to the custom_release_rules. Unfortunately, as the separator : is hardcoded here https://github.com/mathieudutour/github-tag-action/blob/87322e4efff34a7f630512379aabad45e3254d53/src/utils.ts#L76 it's not possible to add them like :zap::patch, :bug::patch, :ambulance::patch, :sparkles::minor etc.. My suggestion would be to either have optional separators with two new parameters (:zap:,patch; :bug:,patch; ...) or to use another data representation of the custom_release_rules. What do you think @mathieudutour ?