Add an API

Server/CalculatorEndpoints.cs

@@ -0,0 +1,15 @@
+namespace GrpcCalculator.Server;
+
+public static class CalculatorEndpoints
+{
+    public static RouteGroupBuilder MapCalculatorApi(this RouteGroupBuilder group)
+    {
+        group.MapPost("/operator/{op}", (
+            CalculatorOperator op,
+            Calculator calculator) => calculator.OperatorPressed(op));
+        group.MapPost("/equals", (Calculator calculator) => calculator.EqualsPressed());
+        group.MapPost("/digit/{digit}", (string digit, Calculator calculator) => calculator.DigitPressed(digit));
+
+        return group;
+    }
+}