chore(model): update text to image input (#137)

Because

- text to image input prompt is required, others fields is optional

This commit

- update text to image input

Author: phelan

vdp/model/v1alpha/task_text_to_image.proto

@@ -8,13 +8,15 @@ import "google/api/field_behavior.proto";
 // TextToImageInput represents the input of text to image task
 message TextToImageInput {
   // The prompt text
-  string prompt = 1 [ (google.api.field_behavior) = OUTPUT_ONLY ];
-  // The steps
-  optional int64 steps = 2 [ (google.api.field_behavior) = OUTPUT_ONLY ];
-  // The guidance scale
-  optional float cfg_scale = 3 [ (google.api.field_behavior) = OUTPUT_ONLY ];
-  // The seed
-  optional int64 seed = 4 [ (google.api.field_behavior) = OUTPUT_ONLY ];
+  string prompt = 1 [ (google.api.field_behavior) = REQUIRED ];
+  // The steps, default is 5
+  optional int64 steps = 2 [ (google.api.field_behavior) = OPTIONAL ];
+  // The guidance scale, default is 7.5
+  optional float cfg_scale = 3 [ (google.api.field_behavior) = OPTIONAL ];
+  // The seed, default is 0
+  optional int64 seed = 4 [ (google.api.field_behavior) = OPTIONAL ];
+  // The number of generated samples, default is 1
+  optional int64 samples = 5 [(google.api.field_behavior) = OPTIONAL ];
 }
 
 // TextToImageOutput represents the output of text to image task