Review complexity of the current generic IOC template

[gilesknap]

In preparation for the EPICS Collaboration Meeting I added the following features to generic IOCs devcontainer:

• allow isolated development in a container network to keep PVs local
• add a gateway to access the above locally
• allow auto-generated bob file access from outside of the container for phoebus

Although these are worthy features there are a couple of problems with the current implementation:

• it has made generic-ioc devcontainer launch much more brittle
  • opi/generated/.placeholder gets deleted by the opi generation and this is easily committed to the repo - breaking the devcontainer
  • the devcontainer fails to start if the 'channel-access' network has not been created.
  • Both of the above cause errors that do not help diagnose the cause
• all of the additional boilerplate should really be factored out into a separate repo

If isolated networking cannot be simplified due to podman user mode networking we could consider other approaches like picking your own CA port.