Make AWM Primary Network Optimization configurable

[martineckardt]

Context and scope When running a Subnet with all validators in partial sync mode, it will not be able to verify incoming messages from the primary network. The optimization will try to gather signatures over the C-Chain's message from the Subnet's validator set. Since these do not sync the C-Chain they won't be able to sign the message.

We should make this optimization configurable.

Discussion and alternatives TBD

Open questions TBD