Joystick: account for pilot input failsafes

[ES-Alexander]

Extension of #713, to avoid accidentally causing a failsafe while also avoiding needless resource wastage:

An ideal solution would account for whether there is a pilot input failsafe configured, and if so send repeated inputs only as often as necessitated by the timeout parameter (to minimise resource wastage). That said, I'm not sure whether non-ArduSub vehicles actually have such a failsafe - could be good to check that, and/or offer the repeated message frequency as a user-configurable parameter.

ArduSub has FS_PILOT_INPUT, with times managed by FS_PILOT_TIMEOUT.

Rover has RC_FS_TIMEOUT, although we should check whether this applies to MANUAL_CONTROL (and RC_CHANNELS_OVERRIDE, for future reference), or if it only applies to real RC input.

Haven't checked other vehicle firmwares, and it's probably worth supporting a manual override in Cockpit since we can't guarantee all vehicles will have such a parameter for a timeout.

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NOTE: autopilot handling of no pilot input is generally separate to how it handles completely losing connection to the control station software (e.g. triggered via a heartbeat/gcs failsafe, like GCS_FS_ENABLE).