FR: `udp` repeat messages

[nagyrobi]

As a method to improve reliability of the channel, we could have a

repeat:
  interval: 50ms
  count: 3

option on the provider side. Sane values could probably be between 10ms and 1s for interval, and 1 to 5 for count.
Mimicking the infrared remotes, some of which repeat single key presses within the protocol to increase reliability.

Care should be taken on the receiver side not to trigger repeated updates for the repeated packet so maybe a provider-side nonce which would be the same in the repeats could be employed for this purpose.

This would let us use a wider update_interval for the entire component, and could offer increased reliability in case of #114.