Docuseal

**Is your feature request related to a problem? Please describe.** As part of the foundation, we often need to sign contracts. In the past we used proprietary services for that, but @imincik recently pointed out https://www.docuseal.com/ and how easy it is to deploy. **Describe the solution you'd like** We'd like to have a self-hosted docuseal instance running on docuseal.nixos.org, with access for the @NixOS/foundation board. **Describe alternatives you've considered** Pay for proprietary services **Additional context** <!-- Add any other context or screenshots about the feature request here. -->