SelfID: Make SELF ID messages optional

[muramura]

1. The SELF ID message is an optional specification.
2. the number of characters in the text is also sent out when the number of characters is 0.
   I make the SELF ID message optional, in accordance with the F3411-22A specification.
   If the number of characters in the text is 0, there is no merit in sending the message.
   and one frame length is 25 bytes longer.
   I will only send out the message when the text is set.
   I will allow SELF ID messages to be set in the configuration parameter.

AFTER:
TEXT LEN > 0

TEXT LEN = 0

[tridge]

@muramura and @BluemarkInnovations Self-ID is marked with an asterix, which means:

the problem is, which jurisdictions? At the moment if not supplied we send a blank message, which seems fine to me. We could omit it, but it adds complexity

[friissoren]

the problem is, which jurisdictions?

At least the rules and additional standardization documents in the US, EU and Japan all keep the Self ID message as optional. Whether any other jurisdiction will make it mandatory can only be speculated upon at this point.

[BluemarkInnovations]

@tridge I think we need to add a region variable to the parameters. This allows to customize the arm_status_check function based on the region. For instance, if the region is set to EU, make the OPEN_DRONE_ID_OPERATOR_ID message mandatory. Otherwise fail the arm_status_check. I can work on such feature in a PR (this month).

In general, I favor not to send black messages.

[tridge]

this is handled by #101