Add EU_433_V2 entry, to facilitate transition

[fifieldt]

When EU_433 was originally defined in firmware, the band definition was off by a small amount.

EU_433 is now in widespread use, so changing that definition is a breaking change. This patch introduces an alternative.

In order to facilitate communities making a planned transition between the frequency bands at a coordinated time, this patch introduces EU_433_V2 . Selecting EU_433_V2 will configure a Meshtastic device with the corrected band definitions.

The overall plan for the transition would look something like this:

1. Introduce EU_433_V2 to protobufs, firmware, and apps
2. Announce that communities have the option of making a transition to the corrected band, and encourage communities to coordinate a transition at a time that works for them.
3. After many months, we reach a time where the supermajority of affected communities have made a transition to the new band
4. We change app behaviour, making EU_433_V2 as the prominent choice over EU_433
5. We monitor complaints about band options and communities with a lagging transition.
6. We remove the original EU_433 from the apps

See also: https://github.com/meshtastic/firmware/pull/2696

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