feat(server): support importing users with password (#11978)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Added support for an optional password field when creating a new user via the user creation form or API.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/schema.gql

@@ -340,6 +340,7 @@ input CreateCopilotPromptInput {
 input CreateUserInput {
   email: String!
   name: String
+  password: String
 }
 
 type CredentialsRequirementType {