Serialsend6 - comma-separated decimal send as binary

[grob6000]

Description:

Alternative to #8920 (i.e. one or the other). Same use case - allowing sending of parameters using rules to binary serial devices e.g. #5737. I've noted that the mqtt response formats in HEX when serial is received after a binary message is sent - I don't think this should change so it's treated the same.

example: serialsend6 255,85,5,5,220,10

An example rule that (should) allow the above device to work with vanilla tasmota + this PR:
rule1
on dimmer#state=0 do event setdimmer=5 endon
on dimmer#state>0 do backlog scale1 %value%,1,100,16,255; event udimmer endon
on dimmer#boot do backlog baudrate 9600; scale1 %value%,1,100,16,255; event udimmer endon
on event#udimmer do event setdimmer=%var1% endon
on event#setdimmer do serialsend6 255,85,%value%,5,220,10 endon
on power1#state=0 do event setdimmer=5 endon
on power1#state=1 do event setdimmer=%var1% endon

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on Tasmota core ESP8266 V.2.7.2.1
• The code change is tested and works on core ESP32 V.1.12.2

no device to test sorry

• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass

[arendst]

Thx. Will evaluate