Bounty sharing consent

For bounty posts, add a Yes/No option or dropdown where the bounty poster need to specify whether they agree with the winning creator to share the model with all Civitai users or whether it should be exclusive to the poster. This way, if Yes is chosen, a consent to share the model is given and there will be no further disputes regarding this in the future. As a counterpart to this, add similar choice to the entry submit forms where any bounty participant has to agree to respect the bounty poster's choice before they can submit their entry. This way people who are not willing to make their model exclusive for the submitter (if they chose that option) will not be able to participate in the bounty.