This is the zulip-flutter counterpart to the following zulip-mobile issue:

• Generate narrow links using "channel" operator, not "stream", if server is recent zulip-mobile#5861

We should do the same thing here.

Like in zulip-mobile, it won't yet be time to do this until a zulip-mobile release with zulip/zulip-mobile#5860 (to recognize the same "channel" operator) has been out to users for some weeks.

Related server/web issues:

• Umbrella issue: Rename "stream" to "channel" zulip#28468
• Specific corresponding issue: Generate narrow links using "channel" operator, not "stream" zulip#30385