Fix Content-Disposition hard-coded to attachments

Due to a regression in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24919,
Content-Disposition is hard-coded to `attachment` instead of `inline`.
We now use the argument `disposition` to fix that problem.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57660

app/controllers/concerns/send_file_upload.rb

@@ -3,7 +3,7 @@
 module SendFileUpload
   def send_upload(file_upload, send_params: {}, redirect_params: {}, attachment: nil, proxy: false, disposition: 'attachment')
     if attachment
-      response_disposition = ::Gitlab::ContentDisposition.format(disposition: 'attachment', filename: attachment)
+      response_disposition = ::Gitlab::ContentDisposition.format(disposition: disposition, filename: attachment)
 
       # Response-Content-Type will not override an existing Content-Type in
       # Google Cloud Storage, so the metadata needs to be cleared on GCS for

spec/controllers/concerns/send_file_upload_spec.rb

@@ -52,6 +52,23 @@ describe SendFileUpload do
       end
     end
 
+    context 'with inline image' do
+      let(:filename) { 'test.png' }
+      let(:params) { { disposition: 'inline', attachment: filename } }
+
+      it 'sends a file with inline disposition' do
+        # Notice the filename= is omitted from the disposition; this is because
+        # Rails 5 will append this header in send_file
+        expected_params = {
+          filename: 'test.png',
+          disposition: "inline; filename*=UTF-8''test.png"
+        }
+        expect(controller).to receive(:send_file).with(uploader.path, expected_params)
+
+        subject
+      end
+    end
+
     context 'with attachment' do
       let(:filename) { 'test.js' }
       let(:params) { { attachment: filename } }