Add price grain generic

src/Managing.Application.Abstractions/Grains/IPriceFetcherGrain.cs

@@ -0,0 +1,18 @@
+using Orleans;
+
+namespace Managing.Application.Abstractions.Grains;
+
+/// <summary>
+/// Orleans grain interface for price fetching operations.
+/// This stateless worker grain handles fetching price data from external APIs 
+/// and publishing to Orleans streams for a specific timeframe.
+/// </summary>
+public interface IPriceFetcherGrain : IGrainWithStringKey
+{
+    /// <summary>
+    /// Fetches price data for all supported exchange/ticker combinations
+    /// and publishes new candles to their respective streams.
+    /// </summary>
+    /// <returns>True if the operation completed successfully, false otherwise</returns>
+    Task<bool> FetchAndPublishPricesAsync();
+}