Extract create_user_messages.
Extract create_user_messages.

The logic to create UserMessage rows when you create a message
is very self-contained, and it's helpful to be able to profile it.

rht/zulip,kou/zulip,kou/zulip,Galexrt/zulip,andersk/zulip,shubhamdhama/zulip,synicalsyntax/zulip,verma-varsha/zulip,jackrzhang/zulip,kou/zulip,tommyip/zulip,rishig/zulip,timabbott/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,synicalsyntax/zulip,hackerkid/zulip,rishig/zulip,eeshangarg/zulip,timabbott/zulip,kou/zulip,amanharitsh123/zulip,kou/zulip,dhcrzf/zulip,rht/zulip,brainwane/zulip,rht/zulip,showell/zulip,tommyip/zulip,amanharitsh123/zulip,rishig/zulip,punchagan/zulip,zulip/zulip,brockwhittaker/zulip,amanharitsh123/zulip,shubhamdhama/zulip,timabbott/zulip,brockwhittaker/zulip,synicalsyntax/zulip,brainwane/zulip,eeshangarg/zulip,mahim97/zulip,rht/zulip,dhcrzf/zulip,timabbott/zulip,mahim97/zulip,dhcrzf/zulip,kou/zulip,dhcrzf/zulip,zulip/zulip,mahim97/zulip,amanharitsh123/zulip,jackrzhang/zulip,jackrzhang/zulip,hackerkid/zulip,amanharitsh123/zulip,kou/zulip,Galexrt/zulip,verma-varsha/zulip,shubhamdhama/zulip,brainwane/zulip,synicalsyntax/zulip,dhcrzf/zulip,eeshangarg/zulip,Galexrt/zulip,tommyip/zulip,zulip/zulip,amanharitsh123/zulip,Galexrt/zulip,jackrzhang/zulip,rht/zulip,eeshangarg/zulip,synicalsyntax/zulip,brockwhittaker/zulip,showell/zulip,showell/zulip,andersk/zulip,rishig/zulip,hackerkid/zulip,Galexrt/zulip,rht/zulip,zulip/zulip,showell/zulip,rishig/zulip,hackerkid/zulip,jackrzhang/zulip,jackrzhang/zulip,Galexrt/zulip,tommyip/zulip,andersk/zulip,mahim97/zulip,brockwhittaker/zulip,andersk/zulip,brockwhittaker/zulip,brockwhittaker/zulip,tommyip/zulip,shubhamdhama/zulip,brainwane/zulip,synicalsyntax/zulip,brainwane/zulip,shubhamdhama/zulip,verma-varsha/zulip,timabbott/zulip,brainwane/zulip,shubhamdhama/zulip,rishig/zulip,hackerkid/zulip,eeshangarg/zulip,rishig/zulip,punchagan/zulip,mahim97/zulip,andersk/zulip,brainwane/zulip,dhcrzf/zulip,verma-varsha/zulip,dhcrzf/zulip,mahim97/zulip,zulip/zulip,eeshangarg/zulip,hackerkid/zulip,punchagan/zulip,timabbott/zulip,jackrzhang/zulip,synicalsyntax/zulip,verma-varsha/zulip,punchagan/zulip,showell/zulip,Galexrt/zulip,verma-varsha/zulip,shubhamdhama/zulip,showell/zulip,tommyip/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,rht/zulip,tommyip/zulip,timabbott/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,showell/zulip