grpc: add shutdown call for external management (#957)

* grpc: add shutdown call for external management

* go mod: tidy

* glorious: suggestion

* Update engine/engine.go

Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

* Update engine/rpcserver.go

Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

* Update main.go

Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>

* Update engine/rpcserver.go

Co-authored-by: Scott <gloriousCode@users.noreply.github.com>

Co-authored-by: Ryan O'Hara-Reid <ryan.oharareid@thrasher.io>
Co-authored-by: Adrian Gallagher <adrian.gallagher@thrasher.io>
Co-authored-by: Scott <gloriousCode@users.noreply.github.com>

gctrpc/rpc.swagger.json

@@ -3042,6 +3042,28 @@
         ]
       }
     },
+    "/v1/shutdown": {
+      "get": {
+        "operationId": "GoCryptoTraderService_Shutdown",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/gctrpcShutdownResponse"
+            }
+          },
+          "default": {
+            "description": "An unexpected error response.",
+            "schema": {
+              "$ref": "#/definitions/rpcStatus"
+            }
+          }
+        },
+        "tags": [
+          "GoCryptoTraderService"
+        ]
+      }
+    },
     "/v1/simulateorder": {
       "post": {
         "operationId": "GoCryptoTraderService_SimulateOrder",
@@ -5346,6 +5368,9 @@
         }
       }
     },
+    "gctrpcShutdownResponse": {
+      "type": "object"
+    },
     "gctrpcSimulateOrderRequest": {
       "type": "object",
       "properties": {