Update Preimages API of pallet Whitelist

[gavofyork]

Instead of using

type PreimageProvider: PreimageProvider<Self::Hash> + PreimageRecipient<Self::Hash>;

it should be

type PreimageProvider: QueryPreimage + StorePreimage;

When using QueryPreimage::fetch(hash: &Hash, len: Option<u32>), make sure that len is Some! This will basically mean that dispatch_whitelisted_call will need to take an extra len: u32 argument.

[muharem]

Solved in the PR #12834