Show channel description in channel link autocomplete

[sm-sayedi]

After #1902, we'll have an autocomplete for channels in the compose box. It will show the channel icon and name, but not the description, which is what this issue is tracking.

See Figma: https://www.figma.com/design/1JTNtYo9memgW7vV6d0ygq/Zulip-Mobile?node-id=7960-31568&t=01sEdRPrUVQ15sVz-0

Related issues

• Prerequisite: content: Support Zulip content outside messages (even outside per-account contexts) #488