openapi: Document `message` event.
openapi: Document `message` event.

showell/zulip,kou/zulip,punchagan/zulip,showell/zulip,eeshangarg/zulip,eeshangarg/zulip,hackerkid/zulip,andersk/zulip,rht/zulip,brainwane/zulip,rht/zulip,brainwane/zulip,andersk/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,brainwane/zulip,hackerkid/zulip,brainwane/zulip,showell/zulip,rht/zulip,hackerkid/zulip,hackerkid/zulip,andersk/zulip,showell/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,showell/zulip,andersk/zulip,zulip/zulip,punchagan/zulip,rht/zulip,zulip/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,zulip/zulip,brainwane/zulip,showell/zulip,brainwane/zulip,rht/zulip,zulip/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,punchagan/zulip,zulip/zulip,rht/zulip,showell/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,punchagan/zulip