FEATURE - ImageMagick jpeg quality (#11004)

* FEATURE - Add SiteSettings to control JPEG image quality

`recompress_original_jpg_quality` - the maximum quality of a newly
uploaded file.

`image_preview_jpg_quality` - the maximum quality of OptimizedImages

spec/lib/upload_creator_spec.rb

@@ -123,6 +123,11 @@ RSpec.describe UploadCreator do
     end
 
     describe 'converting to jpeg' do
+      def image_quality(path)
+        local_path = File.join(Rails.root, 'public', path)
+        Discourse::Utils.execute_command("identify", "-format", "%Q", local_path).to_i
+      end
+
       let(:filename) { "should_be_jpeg.png" }
       let(:file) { file_from_fixtures(filename) }
 
@@ -168,6 +173,21 @@ RSpec.describe UploadCreator do
         expect(File.extname(upload.url)).to eq('.jpeg')
         expect(upload.original_filename).to eq('should_be_jpeg.jpg')
       end
+
+      it 'should alter the image quality' do
+        SiteSetting.png_to_jpg_quality = 75
+        SiteSetting.recompress_original_jpg_quality = 40
+        SiteSetting.image_preview_jpg_quality = 10
+
+        upload = UploadCreator.new(file, filename, force_optimize: true).create_for(user.id)
+
+        expect(image_quality(upload.url)).to eq(SiteSetting.recompress_original_jpg_quality)
+
+        upload.create_thumbnail!(100, 100)
+        upload.reload
+
+        expect(image_quality(upload.optimized_images.first.url)).to eq(SiteSetting.image_preview_jpg_quality)
+      end
     end
 
     describe 'converting HEIF to jpeg' do