[ros2service] call only once by default

[mikaelarguedas]

No description provided.

[dirk-thomas]

Calling a service repeatedly as fast as possible sounds like a reasonable use case to me. Therefore I wouldn't use that to represent "once".

Instead I would suggest to remove the default value of the --rate argument (which makes it None). And pass 1. / args.rate if args.rate else None to the requester function (removing the once argument).

[mikaelarguedas]

Fair enough, updated accordingly