[milo] Add BuildSummary and common models.

milo/api/resp/componenttype_string.go

+// Code generated by "stringer -type=ComponentType"; DO NOT EDIT.
+
+package resp
+
+import "fmt"
+
+const _ComponentType_name = "RecipeStepSummary"
+
+var _ComponentType_index = [...]uint8{0, 6, 10, 17}
+
+func (i ComponentType) String() string {
+        if i < 0 || i >= ComponentType(len(_ComponentType_index)-1) {
+                return fmt.Sprintf("ComponentType(%d)", i)
+        }
+        return _ComponentType_name[_ComponentType_index[i]:_ComponentType_index[i+1]]
+}