Allow specifying custom tags at the route level

The current logic to determine a route's set of tags is based solely on the route, which works in most cases, but isn't flexible when you want to override the tags.

The situation that led me here was the following setup:

```
prefix 'locations/:id'

resource :employees do
  desc 'Retrieve employees for a given location'

  get '/' do
    ...
  end
end
```

Which grouped the `/locations/:id/employees` under the `locations` namespace. This was undesirable, because almost all of the endpoints in our API are prefixed with `/locations/:id`, which meant that they were all grouped under the `locations` namespace.

Allowing an additional `tags` attribute on the `desc` method solved the issue for me.

```
desc 'Retrieve employees for a given location', tags: ['employees']
```

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 * [#520](https://github.com/ruby-grape/grape-swagger/pull/520): Response model can have required attributes - [@WojciechKo](https://github.com/WojciechKo).
 * [#510](https://github.com/ruby-grape/grape-swagger/pull/510): Use 'token_owner' instead of 'oauth_token' on Swagger UI endpoint authorization. - [@texpert](https://github.com/texpert).
-* Your contribution here.
+* [#523](https://github.com/ruby-grape/grape-swagger/pull/523): Allow specifying custom tags at the route level. - [@jordanfbrown](https://github.com/jordanfbrown).
 
 #### Fixes
 

lib/grape-swagger/endpoint.rb

@@ -112,7 +112,7 @@ def method_object(route, options, path)
       method[:parameters]  = params_object(route)
       method[:security]    = security_object(route)
       method[:responses]   = response_object(route, options[:markdown])
-      method[:tags]        = tag_object(route)
+      method[:tags]        = route.options.fetch(:tags, tag_object(route))
       method[:operationId] = GrapeSwagger::DocMethods::OperationId.build(route, path)
       method.delete_if { |_, value| value.blank? }
 

spec/swagger_v2/endpoint_versioned_path_spec.rb

@@ -1,17 +1,21 @@
 require 'spec_helper'
 
 describe 'Grape::Endpoint#path_and_definitions' do
-  let(:api) do
-    item = Class.new(Grape::API) do
+  let(:item) do
+    Class.new(Grape::API) do
       version 'v1', using: :path
 
       resource :item do
         get '/'
       end
     end
+  end
+
+  let(:api) do
+    item_api = item
 
     Class.new(Grape::API) do
-      mount item
+      mount item_api
       add_swagger_documentation add_version: true
     end
   end
@@ -28,4 +32,21 @@
   it 'tags the endpoint with the resource name' do
     expect(subject.first['/v1/item'][:get][:tags]).to eq ['item']
   end
+
+  context 'when custom tags are specified' do
+    let(:item) do
+      Class.new(Grape::API) do
+        version 'v1', using: :path
+
+        resource :item do
+          desc 'Item description', tags: ['special-item']
+          get '/'
+        end
+      end
+    end
+
+    it 'tags the endpoint with the custom tags' do
+      expect(subject.first['/v1/item'][:get][:tags]).to eq ['special-item']
+    end
+  end
 end