Backend image rendering as plugin (#11966)

* rendering: headless chrome progress

* renderer: minor change

* grpc: version hell

* updated grpc libs

* wip: minor progess

* rendering: new image rendering plugin is starting to work

* feat: now phantomjs works as well and updated alerting to use new rendering service

* refactor: renamed renderer package and service to rendering to make renderer name less confusing (rendering is internal service that handles the renderer plugin now)

* rendering: now render key is passed and render auth is working in plugin mode

* removed unneeded lines from gitignore

* rendering: now plugin mode supports waiting for all panels to complete rendering

* fix: LastSeenAt fix for render calls, was not set which causes a lot of updates to Last Seen at during rendering, this should fix sqlite db locked issues in seen in previous releases

* change: changed render tz url parameter to use proper timezone name as chrome does not handle UTC offset TZ values

* fix: another update to tz param generation

* renderer: added http mode to renderer service, new ini setting [rendering] server_url

vendor/cloud.google.com/go/CONTRIBUTORS

@@ -22,6 +22,7 @@ David Symonds <dsymonds@golang.org>
 Filippo Valsorda <hi@filippo.io>
 Glenn Lewis <gmlewis@google.com>
 Ingo Oeser <nightlyone@googlemail.com>
+James Hall <james.hall@shopify.com>
 Johan Euphrosine <proppy@google.com>
 Jonathan Amsterdam <jba@google.com>
 Kunpei Sakai <namusyaka@gmail.com>