Allow case-insensitive ok or OK replies from pluggable discoveries and monitors

[cmaglie]

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  before creating one)
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• Tests for the changes have been added (for bug fixes / features)
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• What kind of change does this PR introduce?
  Allow case-insensitive ok or OK replies from pluggable discoveries and monitors.

What is the current behavior?
If a discovery or a monitor replies to a command, for example, with:

{
  "eventType": "describe",
  "message": "ok",
  "port_description": {
    "protocol": "serial",
    "configuration_parameters": {
    }
  }
}

the answer is treated as an error because it requires a case-sensitive "OK".
Also. the error message is completely useless:

Error getting port settings details: Port monitor error: command 'describe' failed: ok

What is the new behavior?
The response is accepted for any case-insensitive ok / OK

Does this PR introduce a breaking change, and is
titled accordingly?
No breaking changes

[PaulStoffregen]

Looks like eventType parsing is also case sensitive. For example, if I reply with this JSON

{
"eventType": "DESCRIBE",
"message": "OK",
"port_description": {
"protocol": "Teensy",
"configuration_parameters": {
}
}
}

I get this error, which isn't nearly as difficult as the OK issue, since it tells me what it expected.

Error getting port settings details: Port monitor error: communication out of sync, expected 'describe', received 'DESCRIBE'

[cmaglie]

I get this error, which isn't nearly as difficult as the OK issue, since it tells me what it expected.

good point, I've improved the error messages in the same way.