Implement Instruction for *Box wrappers

[nxsaken]

Currently, only InstructionBox implements Instruction out of all ISI wrappers. I expected RegisterBox, MintBox and the rest of the wrappers to be usable with iroha.submit_*() directly, but they are not. I think it would be more ergonomic if they were.

[mversic]

related to #4703

[nxsaken]

Additionally, change instances of impl IntoIterator<Item = impl Instruction> function parameters to impl IntoIterator<Item = I>, I: Instruction, which is more flexible due to the turbofish syntax being available. This would allow wrapping multiple instructions into *Boxes without binding them to a separate variable.