Firmware, Add to the GPAD_API firmware a user menu option to select / deselect flow control on the COM port.

[ForrestErickson]

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The Krake has a COM port. Some devices to which the Krake connects may have COM ports with flow control.
If we do not manage flow control correctly there will not be communication.

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The Krake hardware supports hardware flow control on pins 7 and 9 of the COM port which are RTS and CTS.
Add to the GPAD_API firmware a user menu option to select / deselect flow control on the COM port.

The Hardware Serial library supports flow control.
See this issue for information and example of set up for hardware flow control:
espressif/arduino-esp32#12199 (comment)
See example code at: https://github.com/espressif/arduino-esp32/blob/master/tests/validation/uart/uart.ino#L516

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For testing flow control a DB9 loop back adapter will be required.
The loop back will connect pins 2 to 3 and pins 7 to 8.

[ForrestErickson]

CC: @nk25719 @ForrestErickson

This flow control assumes a buffer of memory and some kind of test for that buffer size should be contemplated too.