add ddpm scheduler

ddpm_scheduler/scheduler_config.json

@@ -0,0 +1,16 @@
+{
+  "_class_name": "DDPMScheduler",
+  "_diffusers_version": "0.18.0.dev0",
+  "beta_end": 0.012,
+  "beta_schedule": "linear",
+  "beta_start": 0.00085,
+  "clip_sample": true,
+  "clip_sample_range": 2.0,
+  "dynamic_thresholding_ratio": 0.995,
+  "num_train_timesteps": 1000,
+  "prediction_type": "epsilon",
+  "sample_max_value": null,
+  "thresholding": true,
+  "trained_betas": null,
+  "variance_type": "learned_range"
+}