`ethexe`: extend rpc API to be able to access announces outcome directly

[grishasobol]

Problem

current client

#[cfg_attr(not(feature = "client"), rpc(server))]
#[cfg_attr(feature = "client", rpc(server, client))]
pub trait Block {
    #[method(name = "block_header")]
    async fn block_header(&self, hash: Option<H256>) -> RpcResult<(H256, BlockHeader)>;

    #[method(name = "block_events")]
    async fn block_events(&self, block_hash: Option<H256>) -> RpcResult<Vec<BlockRequestEvent>>;

    #[method(name = "block_outcome")]
    async fn block_outcome(&self, block_hash: Option<H256>) -> RpcResult<Vec<StateTransition>>;
}

should be at least more

announce_outcome
announce_by_hash
announce_program_states