Added "rts" and "dtr" configuration parameters.

[cmaglie]

This PR adds the rts and cts configuration parameter that allows to set and reset RTS and CTS lines.

[per1234]

UPDATE: fixed!

The port is always configured as dtr=on,rts=off after the change made in 37305bb

For example, any of the following commands:

$ arduino-cli monitor -p COM43 --config dtr=off,rts=off

$ arduino-cli monitor -p COM43 --config dtr=on,rts=on

$ arduino-cli monitor -p COM43 --config dtr=off,rts=on

Produce these states:

I only checked on Windows. Everything works as expected for me with the version from 4d98996

[cmaglie]

Thanks for testing it @per1234, I messed up with the control bits, now I pushed a new tentative fix in 16a3ef6 (EDIT: just rebased over CI workflow fix)

[per1234]

Everything is working as expected on Windows and Linux with the build from 16a3ef6