add method: fn send_xt<C: Encode>(xt: UncheckedExtrinsic<C>, xt_status: XtStatus)

[clangenb]

We always hex encode extrinsics on our own before sending them.

we could use sp_core::Bytes type as parameter type to the json requests = Struct Bytes(Vec<u8>), which has custom serialization that prepends 0x. Then we can simply pass the encoded value of the extrinsic

[clangenb]

Actually, I think we should just add a method (don't remove the current one accepting a string):

fn send_xt<C: Encode>(xt: UncheckedExtrinsic<C>, xt_status: XtStatus)

This will remove some boilerplate code on the caller site.

Then we could also run some validation against the metadata before sending.

[haerdib]

I think the validation should happen during the call creation, not the sending. See #416

What do you think?