Check user-groups permissions before offering "Mark as resolved"

[chrisbobbe]

From the Help Center doc on the "Mark as resolved" feature:

https://zulip.com/help/resolve-a-topic

Users can resolve and unresolve a topic if they have permission to edit topics. Organization administrators can configure who can edit topics.

If the user doesn't have permission to resolve/unresolve a topic, we shouldn't offer the button for it, because it takes up space and will always show a server error when they tap it (maybe after making them wait a while on a slow connection).

I've left this out of my work on #744 for expediency; the button is just always offered. The client-side permission check is also not implemented in the legacy RN app.

We're transitioning to a new permissions system based on user groups:

• Implement group-based permission checks #814

Let's plan to implement this just in that new system, skipping the old system, so we don't have to implement it twice. That'll just mean giving the same behavior as the legacy RN app until the server is upgraded to version 10 or later.

[alya]

Note the ongoing work to build a dedicated permission: zulip/zulip#21811 / zulip/zulip#21811.

In the future, I expect this to additionally be controlled by a per-channel permission (details TBD).