feat: add shared filter to workspaces query (#19807)

Adds a `shared:<boolean>` search query to the `/workspaces [get]`
endpoint


https://github.com/user-attachments/assets/ccf84bd9-c1fd-4085-825b-2e3176a2d488

Closes
[coder/internal#972](https://github.com/coder/internal/issues/972)

coderd/database/modelqueries.go

@@ -275,6 +275,7 @@ func (q *sqlQuerier) GetAuthorizedWorkspaces(ctx context.Context, arg GetWorkspa
 		arg.UsingActive,
 		arg.HasAITask,
 		arg.HasExternalAgent,
+		arg.Shared,
 		arg.RequesterID,
 		arg.Offset,
 		arg.Limit,