[Feature]: Add Async/Await support in Cortex.States

[eneshoxha]

New async interface

We are introducing IAsyncDataStore for not introducing a breaking change in IDataSource

public interface IAsyncDataStore<TKey, TValue> : IDataStore<TKey, TValue>
{
    ValueTask<TValue?> GetAsync(
        TKey key,
        CancellationToken cancellationToken = default);

    ValueTask PutAsync(
        TKey key,
        TValue value,
        CancellationToken cancellationToken = default);

    ValueTask<bool> ContainsKeyAsync(
        TKey key,
        CancellationToken cancellationToken = default);

    ValueTask RemoveAsync(
        TKey key,
        CancellationToken cancellationToken = default);

#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_0_OR_GREATER
    IAsyncEnumerable<KeyValuePair<TKey, TValue>> GetAllAsync(
        CancellationToken cancellationToken = default);

    IAsyncEnumerable<TKey> GetKeysAsync(
        CancellationToken cancellationToken = default);
#endif

    ValueTask<IDictionary<TKey, TValue>> GetManyAsync(
        IEnumerable<TKey> keys,
        CancellationToken cancellationToken = default);

    ValueTask PutManyAsync(
        IEnumerable<KeyValuePair<TKey, TValue>> items,
        CancellationToken cancellationToken = default);
}