add ability to monitor device on second serial port

[mkinney]

Describe the bug Add the ability to monitor the hardware via a second serial port, so we can capture information when there is an issue (like a reboot/lock up)

To Reproduce Steps to reproduce the behavior:

1. Connect to hardware using USB connection.
2. Connect to hardware using a different USB connection.
3. Run meshtastic cli thru first port.
4. Run/Show SerialConsole on second port.

Expected behavior All debug output should go to 2nd serial port.

By default the Heltec nor T-Echo do not have a 2nd physical port, but they can be added by wiring up something like https://smile.amazon.com/gp/product/B01N47LXRA using https://circuits4you.com/2018/12/31/esp32-hardware-serial2-example/ as a guide

Device info:

• Device model: HELTEC21 and TBEAM (not sure if TECHO has capablity)
• Software Version: N/A

Additional context Having this capability might help to troubleshoot intermittent issues and find the source of the problems.

[mkinney]

After thinking about this for a bit, if we had this... we could do a soak-test where we run the same tests over and over until we see failure(s).

[garthvh]

This already works with an external serial module, I can monitor on one and use the CLI on another