Implement transaction comments

Transaction comments can be implemented on gdev network even the final solution in g1 production network will be a bit different. For now, we will only do onchain transaction comments in clear. Offchain and encrypted comments will use the same principle and can be handled later on, after the migration.

See here for implementation discussions and implementation demo: https://forum.duniter.org/t/implementation-des-commentaires-de-transaction/12289.

See here for an implementation example: https://git.duniter.org/clients/rust/gcli-v2s/-/blob/f82fc17ac749ca11012605ea0d80cb8febe0e088/src/commands/commented.rs#L99-124

The idea is to use a utility.batch call wrapping a balances.transfer and a system.remark call.