Document sobridge alongside the soauth network settings

sobridge carries most containers but held no annotation, so it was absent from
the config tree entirely. Its pillar entry is an empty map, so annotating it
adds a setting with no children for docker.networks.soauth.range to collide
with, and the tree still builds.

docker.map.jinja fills in sobridge's range and gateway at render time from
docker.range and docker.gateway, and resets the entry when it is not a mapping,
so nothing writes keys underneath it.

The sentence about sobridge is dropped from the soauth range description now
that sobridge documents itself.

salt/docker/soc_docker.yaml

@@ -8,13 +8,20 @@ docker:
     helpLink: docker
     advanced: True
   networks:
+    sobridge:
+      description: |
+        The default docker network, carrying most containers. Its range and gateway are taken
+        from the docker.range and docker.gateway settings above rather than set here.
+      helpLink: docker
+      readonly: True
+      advanced: True
+      global: True
     soauth:
       range:
         description: |
-          IP range for the soauth docker network. soauth is an isolated network for the
-          authentication services, so that the Kratos and Hydra admin APIs are only reachable
-          from the containers placed on it. Most containers instead use sobridge, which takes
-          its range and gateway from the docker.range and docker.gateway settings above.
+          IP range for the soauth docker network, an isolated network for the authentication
+          services, so that the Kratos and Hydra admin APIs are only reachable from the
+          containers placed on it.
         helpLink: docker
         readonly: True
         advanced: True