[#24] Client: Implement pool part1

first iteration - base classes and methods

Signed-off-by: Pavel Gross <p.gross@yadro.com>

src/FrostFS.SDK.ClientV2/Parameters/IContext.cs

@@ -7,5 +7,5 @@ public interface IContext
     /// callbacks, interceptors.
     /// </summary>
     /// <value>Additional parameters for calling the method</value>
-    Context? Context { get; set; }
+    CallContext? Context { get; set; }
 }