feat: backend support for creating and storing service accounts (#22698)

Add is_service_account column to users table with CHECK constraints
enforcing login_type='none' and empty email for service accounts.
Update user creation API to validate service account constraints.

Related to:
https://linear.app/codercom/issue/PLAT-27/feat-backend-support-for-creating-and-storing-service-accounts

coderd/database/modelmethods.go

@@ -663,20 +663,21 @@ func ConvertUserRows(rows []GetUsersRow) []User {
 	users := make([]User, len(rows))
 	for i, r := range rows {
 		users[i] = User{
-			ID:             r.ID,
-			Email:          r.Email,
-			Username:       r.Username,
-			Name:           r.Name,
-			HashedPassword: r.HashedPassword,
-			CreatedAt:      r.CreatedAt,
-			UpdatedAt:      r.UpdatedAt,
-			Status:         r.Status,
-			RBACRoles:      r.RBACRoles,
-			LoginType:      r.LoginType,
-			AvatarURL:      r.AvatarURL,
-			Deleted:        r.Deleted,
-			LastSeenAt:     r.LastSeenAt,
-			IsSystem:       r.IsSystem,
+			ID:               r.ID,
+			Email:            r.Email,
+			Username:         r.Username,
+			Name:             r.Name,
+			HashedPassword:   r.HashedPassword,
+			CreatedAt:        r.CreatedAt,
+			UpdatedAt:        r.UpdatedAt,
+			Status:           r.Status,
+			RBACRoles:        r.RBACRoles,
+			LoginType:        r.LoginType,
+			AvatarURL:        r.AvatarURL,
+			Deleted:          r.Deleted,
+			LastSeenAt:       r.LastSeenAt,
+			IsSystem:         r.IsSystem,
+			IsServiceAccount: r.IsServiceAccount,
 		}
 	}