docs: Add a new build phase SETUPBUILD for timing information (#142)

PiperOrigin-RevId: 387362210

Source-Link: googleapis/googleapis@760b5d8

Source-Link: googleapis/googleapis-gen@db3c7df

google/cloud/devtools/cloudbuild_v1/types/cloudbuild.py

@@ -569,9 +569,10 @@ class Build(proto.Message):
             Output only. Stores timing information for phases of the
             build. Valid keys are:
 
-            -  BUILD: time to execute all build steps
+            -  BUILD: time to execute all build steps.
             -  PUSH: time to push all specified images.
             -  FETCHSOURCE: time to fetch source.
+            -  SETUPBUILD: time to set up build.
 
             If the build does not specify source or images, these keys
             will not be included.