candidate_pending_availability: RuntimeDescriptor<[para_id: number], {
    commitments: {
        head_data: Binary;
        horizontal_messages: {
            data: Binary;
            recipient: number;
        };
        hrmp_watermark: number;
        new_validation_code: Binary | undefined;
        processed_downward_messages: number;
        upward_messages: Binary;
    };
    descriptor: {
        collator: FixedSizeBinary<32>;
        erasure_root: FixedSizeBinary<32>;
        para_head: FixedSizeBinary<32>;
        para_id: number;
        persisted_validation_data_hash: FixedSizeBinary<32>;
        pov_hash: FixedSizeBinary<32>;
        relay_parent: FixedSizeBinary<32>;
        signature: FixedSizeBinary<64>;
        validation_code_hash: FixedSizeBinary<32>;
    };
} | undefined>

Get the receipt of a candidate pending availability. This returns Some for any paras assigned to occupied cores in availability_cores and None otherwise.