openapi: Add enum for stream role.
openapi: Add enum for stream role.

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