Set Kusto wait encoding to UTF8

The Kusto wait strategy uses the default encoding. For .NET Framework, this resolves to Windows-1252, which causes the Kusto emulator to return a 415 Media Type not Supported error. In .NET Core, it is UTF-8.

This allows .NET Framework tests to run by setting the encoding to always be UTF-8.

Author: MattKotsenas

src/Testcontainers.Kusto/KustoBuilder.cs

@@ -52,7 +52,7 @@ protected override KustoBuilder Init()
                 .WithMethod(HttpMethod.Post)
                 .ForPort(KustoPort)
                 .ForPath("/v1/rest/mgmt")
-                .WithContent(() => new StringContent("{\"csl\":\".show cluster\"}", Encoding.Default, "application/json"))));
+                .WithContent(() => new StringContent("{\"csl\":\".show cluster\"}", Encoding.UTF8, "application/json"))));
     }
 
     /// <inheritdoc />
@@ -72,4 +72,4 @@ protected override KustoBuilder Merge(KustoConfiguration oldValue, KustoConfigur
     {
         return new KustoBuilder(new KustoConfiguration(oldValue, newValue));
     }
-}
+}