Correctly indent quotes in new issue description

By using `>`-quote style instead of `>>>`.

Also: Update documentation images.

app/services/issues/build_service.rb

@@ -43,7 +43,8 @@ module Issues
       discussion_info << " (+#{other_note_count} #{'comment'.pluralize(other_note_count)})" if other_note_count > 0
 
       note_without_block_quotes = Banzai::Filter::BlockquoteFenceFilter.new(first_note.note).call
-      quote = ">>>\n#{note_without_block_quotes}\n>>>"
+      spaces = ' ' * 4
+      quote = note_without_block_quotes.lines.map { |line| "#{spaces}> #{line}" }.join
 
       [discussion_info, quote].join("\n\n")
     end

spec/services/issues/build_service_spec.rb

@@ -57,11 +57,11 @@ describe Issues::BuildService, services: true do
                     "with a blockquote\n"\
                     "> That has a quote\n"\
                     ">>>\n"
-        note_result = "This is a string\n"\
-                    "> with a blockquote\n"\
-                    "> > That has a quote\n"
+        note_result = "    > This is a string\n"\
+                      "    > > with a blockquote\n"\
+                      "    > > > That has a quote\n"
         discussion = Discussion.new([create(:diff_note_on_merge_request, note: note_text)])
-        expect(service.item_for_discussion(discussion)).to include(">>>\n#{note_result}\n>>>")
+        expect(service.item_for_discussion(discussion)).to include(note_result)
       end
     end