Add product categories CQRS handlers and gRPC endpoints

src/Protobufs/BackOffice.BFF.Products.Protobuf/Protos/products.proto

@@ -60,6 +60,19 @@ service ProductsContract
       body: "*"
     };
   };
+
+  rpc GetCategories(GetCategoriesRequest) returns (GetCategoriesResponse){
+    option (google.api.http) = {
+      get: "/GetCategories"
+    };
+  };
+
+  rpc UpdateProductCategories(UpdateProductCategoriesRequest) returns (google.protobuf.Empty){
+    option (google.api.http) = {
+      post: "/UpdateProductCategories"
+      body: "*"
+    };
+  };
 }
 
 message ImageFileModel
@@ -233,3 +246,26 @@ message RemoveProductImageRequest
 {
   int64 product_gallery_id = 1;
 }
+
+message CategoryItem
+{
+  int64 id = 1;
+  string title = 2;
+  bool selected = 3;
+}
+
+message GetCategoriesRequest
+{
+  int64 product_id = 1;
+}
+
+message GetCategoriesResponse
+{
+  repeated CategoryItem items = 1;
+}
+
+message UpdateProductCategoriesRequest
+{
+  int64 product_id = 1;
+  repeated int64 category_ids = 2;
+}