Decide attached gas based on transaction type

[saketh-are]

Currently we attach the maximum of 300 Tgas to every outgoing transaction:

mpc/node/src/indexer/transaction.rs

Lines 40 to 45 in 2ff7716

	let action = FunctionCallAction {
	method_name,
	args,
	gas: 300000000000000,
	deposit: 0,
	};

As a result, we are able to send fewer respond txs before running into congestion limits. Based on testing respond calls consume only 7.62 Tgas, so we should lower the attached gas to 10 Tgas.

We have introduced other types of outgoing transactions as well, which may consume more or less gas:

mpc/node/src/indexer/response.rs

Lines 124 to 133 in 2ff7716

	pub enum ChainSendTransactionRequest {
	Respond(ChainRespondArgs),
	// TODO(#150): Implement join.
	#[allow(dead_code)]
	Join(ChainJoinArgs),
	VotePk(ChainVotePkArgs),
	// TODO(#43): Implement vote_reshared.
	#[allow(dead_code)]
	VoteReshared(ChainVoteResharedArgs),
	}

The attached gas should be decided based on the transaction type.