This PR adds a dedicated error message with instructions when a service URL is missing (federated projects) thanks to the recently added `SchemaPublishMissingUrlError` type.
- Removes the uniqueness requirement of commit it
- Makes the logic of schema publishing simpler and more readable
- Updating the service url results in a new version (previously an update of existing version)
- Introduces a requirement of defining service url in federated projects (new `SchemaPublishMissingUrlError` type)
- Removes the uniqueness requirement of commit it
- Makes the logic of schema publishing simpler and more readable
- Updating the service url results in a new version (previously na update of existing version)
- Introduces a requirement of defining service url in federated projects (new `SchemaPublishMissingUrlError` type)
