api: Fix OpenAPI type declarations for events_register.
api: Fix OpenAPI type declarations for events_register.

A few fields that are actually arrays were incorrectly declared as
strings.

zulip/zulip,brainwane/zulip,timabbott/zulip,rht/zulip,timabbott/zulip,brainwane/zulip,shubhamdhama/zulip,tommyip/zulip,tommyip/zulip,kou/zulip,synicalsyntax/zulip,hackerkid/zulip,brainwane/zulip,synicalsyntax/zulip,hackerkid/zulip,hackerkid/zulip,shubhamdhama/zulip,zulip/zulip,synicalsyntax/zulip,tommyip/zulip,hackerkid/zulip,showell/zulip,eeshangarg/zulip,kou/zulip,showell/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,rht/zulip,hackerkid/zulip,punchagan/zulip,showell/zulip,eeshangarg/zulip,eeshangarg/zulip,showell/zulip,punchagan/zulip,andersk/zulip,shubhamdhama/zulip,tommyip/zulip,timabbott/zulip,kou/zulip,brainwane/zulip,synicalsyntax/zulip,showell/zulip,zulip/zulip,zulip/zulip,andersk/zulip,shubhamdhama/zulip,shubhamdhama/zulip,hackerkid/zulip,rht/zulip,punchagan/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,timabbott/zulip,timabbott/zulip,punchagan/zulip,synicalsyntax/zulip,shubhamdhama/zulip,hackerkid/zulip,zulip/zulip,showell/zulip,andersk/zulip,andersk/zulip,timabbott/zulip,showell/zulip,andersk/zulip,brainwane/zulip,andersk/zulip,shubhamdhama/zulip,brainwane/zulip,punchagan/zulip,kou/zulip,eeshangarg/zulip,tommyip/zulip,kou/zulip,eeshangarg/zulip,tommyip/zulip,rht/zulip,andersk/zulip,timabbott/zulip,zulip/zulip,synicalsyntax/zulip,tommyip/zulip,rht/zulip,brainwane/zulip,synicalsyntax/zulip