push_notification: Add uses_notification_bouncer().
push_notification: Add uses_notification_bouncer().

This function abstracts the logic to ascertain if we are using
notification bouncer service or not. Makes our code more
maintainable.

timabbott/zulip,tommyip/zulip,synicalsyntax/zulip,andersk/zulip,amanharitsh123/zulip,kou/zulip,ryanbackman/zulip,zulip/zulip,dhcrzf/zulip,synicalsyntax/zulip,eeshangarg/zulip,shubhamdhama/zulip,rishig/zulip,dhcrzf/zulip,j831/zulip,Galexrt/zulip,timabbott/zulip,shubhamdhama/zulip,zulip/zulip,rishig/zulip,hackerkid/zulip,shubhamdhama/zulip,kou/zulip,ryanbackman/zulip,j831/zulip,hackerkid/zulip,mahim97/zulip,brainwane/zulip,mahim97/zulip,Galexrt/zulip,amanharitsh123/zulip,christi3k/zulip,timabbott/zulip,Galexrt/zulip,showell/zulip,mahim97/zulip,brockwhittaker/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,kou/zulip,ryanbackman/zulip,showell/zulip,dhcrzf/zulip,brockwhittaker/zulip,Galexrt/zulip,kou/zulip,jackrzhang/zulip,eeshangarg/zulip,tommyip/zulip,ryanbackman/zulip,synicalsyntax/zulip,rht/zulip,dhcrzf/zulip,synicalsyntax/zulip,verma-varsha/zulip,tommyip/zulip,verma-varsha/zulip,jrowan/zulip,synicalsyntax/zulip,rht/zulip,jackrzhang/zulip,timabbott/zulip,vabs22/zulip,christi3k/zulip,jphilipsen05/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,jphilipsen05/zulip,shubhamdhama/zulip,vaidap/zulip,shubhamdhama/zulip,andersk/zulip,tommyip/zulip,rishig/zulip,showell/zulip,eeshangarg/zulip,showell/zulip,rht/zulip,jackrzhang/zulip,jackrzhang/zulip,j831/zulip,verma-varsha/zulip,zulip/zulip,rishig/zulip,amanharitsh123/zulip,zulip/zulip,ryanbackman/zulip,showell/zulip,andersk/zulip,christi3k/zulip,Galexrt/zulip,verma-varsha/zulip,tommyip/zulip,eeshangarg/zulip,jrowan/zulip,andersk/zulip,kou/zulip,amanharitsh123/zulip,mahim97/zulip,jrowan/zulip,hackerkid/zulip,jrowan/zulip,punchagan/zulip,dhcrzf/zulip,mahim97/zulip,vaidap/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,amanharitsh123/zulip,timabbott/zulip,rishig/zulip,brainwane/zulip,vabs22/zulip,vabs22/zulip,hackerkid/zulip,brainwane/zulip,brockwhittaker/zulip,verma-varsha/zulip,vaidap/zulip,vabs22/zulip,punchagan/zulip,brockwhittaker/zulip,rht/zulip,christi3k/zulip,vaidap/zulip,mahim97/zulip,zulip/zulip,kou/zulip,dhcrzf/zulip,jphilipsen05/zulip,punchagan/zulip,tommyip/zulip,Galexrt/zulip,shubhamdhama/zulip,synicalsyntax/zulip,punchagan/zulip,brainwane/zulip,christi3k/zulip,jackrzhang/zulip,rishig/zulip,eeshangarg/zulip,jphilipsen05/zulip,Galexrt/zulip,j831/zulip,rishig/zulip,rht/zulip,showell/zulip,brainwane/zulip,punchagan/zulip,andersk/zulip,vabs22/zulip,jrowan/zulip,hackerkid/zulip,dhcrzf/zulip,rht/zulip,brainwane/zulip,jackrzhang/zulip,shubhamdhama/zulip,kou/zulip,showell/zulip,amanharitsh123/zulip,timabbott/zulip,brainwane/zulip,jphilipsen05/zulip,j831/zulip,jphilipsen05/zulip,jackrzhang/zulip,brockwhittaker/zulip,vabs22/zulip,timabbott/zulip,tommyip/zulip,christi3k/zulip,rht/zulip,j831/zulip,verma-varsha/zulip,brockwhittaker/zulip,jrowan/zulip,ryanbackman/zulip,vaidap/zulip,synicalsyntax/zulip,vaidap/zulip