A network pre-created by the util carried only the compose labels, so
`docker stack deploy` could not recognise it as belonging to the stack:
`getStackNetworks` filters on `com.docker.stack.namespace`, finds nothing,
and the deploy retries the create and aborts with "network with name
<entity> already exists".
This is reachable whenever a network is pre-created for a role whose stack
has not deployed yet. web-app-prometheus does exactly that for every
native-metrics app, which broke the swarm deploy of web-app-openbao.
Stamping the namespace label makes the owning stack adopt the existing
network instead of recreating it. Verified against docker 29.1.3 on a
throwaway swarm: without the label the deploy fails as above, with it the
stack adopts the same network id, and an external consumer stack deploying
with --prune leaves the network intact.
evangelostsak
dc6aeee471