Move EventSource to use a SharedWorker. This prevents issues with HTTP/1.1
open browser connections from preventing gitea from opening multiple tabs.
Also allow setting EVENT_SOURCE_UPDATE_TIME to disable EventSource updating
Fix#11978
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
