Add a macro for complexes multiparts

This will allow to describe multipart in a short way, like JSON payload:

Before:

    put 'Creates a blog with thumbnail' do
      consumes 'multipart/form-data'
      parameter name: :title, in: :formData, type: :string, required: true
      parameter name: :content, in: :formData, type: :string, required: true
      parameter name: :file, in: :formData, type: :file, required: true

      let(:blog) { FactoryBot.build(:blog) }
      let(:title) { blog.title }
      let(:content) { blog.content }
      let(:file) { blog.file }

      ...
    end

After:

    put 'Creates a blog with thumbnail' do
      consumes 'multipart/form-data'
      parameter name: :blog, in: :formData, schema: { '$ref' => '#/definitions/blog' }

      let(:blog) { FactoryBot.attributes_for(:blog) }

      ...
    end

Your mileage may vary but you can always choose the best option.

rswag-specs/spec/rswag/specs/request_factory_spec.rb

@@ -178,6 +178,20 @@ module Rswag
               )
             end
           end
+
+          context 'smart form payload' do
+            before do
+              metadata[:operation][:consumes] = ['multipart/form-data']
+              metadata[:operation][:parameters] = [{ name: 'comment', in: :formData, schema: { type: 'object' } }]
+              allow(example).to receive(:comment).and_return(text: 'Some comment')
+            end
+
+            it 'sets payload to hash of names and example values' do
+              expect(request[:payload]).to eq(
+                :text => 'Some comment'
+              )
+            end
+          end
         end
 
         context 'produces content' do