Distribution: Add FlowForge to Cloud Marketplaces

### Description

All major cloud providers have a marketplace:

- [x] AWS: https://aws.amazon.com/marketplace
- [ ] GCP: https://cloud.google.com/marketplace
- [ ] Azure: https://azuremarketplace.microsoft.com/en-us/home
- [x] DO: https://marketplace.digitalocean.com/

And many more, which might be an interesting way to distribute FlowForge, both Premium and Open-Source.

Start by reviewing the existing AWS and DigitalOcean marketplace distribution and the linked GCP and Azure marketplace entry points. Define which FlowForge editions and marketplace providers are in scope, then consider the work complete when the selected marketplace listings are published and the issue checklist is updated.

Written by the indexing model from the issue text.