Added docs for the tree api (#5834)

* Added docs for the tree api

* Added missing response definition

* Fixed swagger docs

routers/api/v1/swagger/repo.go

@@ -133,3 +133,10 @@ type swaggerResponseAttachment struct {
 	//in: body
 	Body api.Attachment `json:"body"`
 }
+
+// GitTreeResponse
+// swagger:response GitTreeResponse
+type swaggerGitTreeResponse struct {
+	//in: body
+	Body api.GitTreeResponse `json:"body"`
+}