dodal connect cannot selectively mock devices when device_factory has been configured to mock specific devices

On p38 we have a selection of devices that we always want to be backed by simulated backends: optical components that are a clone of the setup on i22 so the output of the beamline can be representative of the output on i22.

When we use `dodal connect`, we can pass True or False for the `--sim-backend` argument- which then overrules what configuration has been set on the beamline module.

## Acceptance Criteria
- [ ] On p38 we can have devices that should be mocked by default
- [ ] When dodal connect is called for p38 with no argument to `--sim-backend`, the devices that should be mocked by default are connected to mock backends, and other devices connect to real backends
- [ ] There is exactly one documented way to achieve this behaviour