Show all workspaces (even with no boards) in the workspace picker

[chenilim]

Summary:
The Workspace Switcher (in PR #1052) currently only returns workspaces (channels the user is a member of) with one or more boards. Let's change this to:

• Return all user channels (even with no boards) instead, and
• Display workspaces with no boards below the ones that do in the dropdown

How important this is to me and why:

Importance: High

The main reason for this is so users can create boards in workspaces (channels) that don't currently have boards, without needing to switch to the Channels UI.

Additional context / similar features:
Discussed in the Sep 2 Dev meeting, and is a step towards the v6.0 nav update spec.

[chenilim]

Filing this issue to track as discussed @harshilsharma63. FYI @asaadmahmood, @sbishel, @ogi-m.

[harshilsharma63]

I'll be working on this independent of the original workspace switcher. That once can be tested and merged while this one continues in development.