Add speeduptransaction RPC method

[lontivero]

This PR adds the speeduptransaction RPC method which received the hash of the transaction to be speed up and returns the raw transaction that does it (using RBF or CPFP) the previous tx.

$ curl -s --user rpcuser:rpcpassword \
--data-binary '{"jsonrpc":"2.0", "id":"curltext", "method":"speeduptransaction", "params":["0f5cdf64a4138d7bbf95bdaf7b73619aae9137085edf69c057b18ff6dda1935f"]}' -H \
-- 'content-type: text/plain;' \
http://127.0.0.1:37128/TestNet%20Small/

This one and #11536 close: #11500

[MarnixCroes]

tack f489f63

any specific reason to not automatically broadcast it?
for me it feels more intuitive to have the tx automatically broadcasted

[lontivero]

any specific reason to not automatically broadcast it?

Yes. It is not possible to know whether the user wants to broadcast it or not, or when.