Use volume mounts for docker/podman

[mfarina1]

Use volume mounts to avoid needing to rebuild images when making configuration changes. This can be simplified from what David Edell prototyped into just documentation (or commented lines in the compose file) to aide developers to preserve the self-contained built images approach Brian Sipos mentioned while still providing a reference for easy usage when needed. The ion configuration file is probably the single file most likely to need overriding for specific tests.

[mfarina1]

This represents an explanation within the product guide about how to do this on a development host. The deployment host won't not have the full source tree available.