add scaled_linear schedule in DDIM

src/diffusers/schedulers/scheduling_ddim.py

@@ -71,6 +71,9 @@ class DDIMScheduler(SchedulerMixin, ConfigMixin):
 
         if beta_schedule == "linear":
             self.betas = np.linspace(beta_start, beta_end, timesteps, dtype=np.float32)
+        elif beta_schedule == "scaled_linear":
+            # this schedule is very specific to the latent diffusion model.
+            self.betas = np.linspace(beta_start**0.5, beta_end**0.5, timesteps, dtype=np.float32) ** 2
         elif beta_schedule == "squaredcos_cap_v2":
             # Glide cosine schedule
             self.betas = betas_for_alpha_bar(timesteps)