Agenda: StorageDescriptor<[Key: number], {
    call: PreimagesBounded;
    maybe_id: FixedSizeBinary<32> | undefined;
    maybe_periodic: FixedSizeArray<2, number> | undefined;
    origin: PolkadotRuntimeOriginCaller;
    priority: number;
} | undefined, false>

Items to be executed, indexed by the block number that they should be executed on.