Function get_local_keys 

pub async fn get_local_keys(
    database: &mut DefaultDb,
    requester: Option<&UserId>,
    requested_keys: BTreeMap<OwnedUserId, Vec<OwnedDeviceId>>,
) -> Result<UsersKeys, InternalServerError>

Gets identity keys for local users, along their signatures.

This function will filter-in keys and signatures the given requester is allowed to see.

NOTE: Use RawUserKeys::try_from() to convert these database keys to raw keys (ready for API responses).