We used to update timestamp in the deployment environment field
in order to trigger a rolling update when the function referenced
resources get updated. However, use timestamp means we are not
able to avoid triggering a rolling update when executor tries to adopt
orphaned deployment due to timestamp changed which is unwanted.
In order to let executor adopt deployment without triggering a rolling
update, we need an identical way to get a value that can reflect res-
ources changed without affecting by time.
To achieve this goal, the sum of the resource version of all referenced
resources is a good fit for our scenario since the sum of the resource
version is always the same as long as no resources changed.
