Assume option_channel_type

[carlaKC]

As outlined in lightning/bolts#1232, this feature bit has been deployed for along time and can be assumed.

Require Feature Bit

• Flip the feature bit to required in provided_init_features to start advertising the feature as required.

Assume Feature Bit

• Fail channel negotiation if channel_type is not set
• Stop advertising the feature bit

[carlaKC]

@elnosh was interested in picking this up, I'll be first reviewer.

@TheBlueMatt do you want to go straight to assuming the feature, or should we first flip it to required and get that into a release?

[TheBlueMatt]

I don't have a strong opinion, maybe we just go straight for it to save on extra PRs later?