Add "Patch Set Description" textbox to push dialog

[monitorlizard]

In Gerrit 3.4 patch set descriptions can no longer be added/edited in the browser.
However, there is a feature to add a patch set description when pushing. It is documented here https://gerrit-review.googlesource.com/Documentation/user-upload.html#patch_set_description

Feature Request:
To include a textbox in the push dialog (e.g. after "Hashtag", see screenshot below) where this patch set description can be entered.
In larger change sets it can be very valuable to label and explain a patchset (e.g. automatic refactorings etc.).

Thanks a lot!