[Suggestion] Add another "Open Workspace" button in the notification if add Docker files without workspace

[v-ruizh]

OS: Windows 10
Build Version: 20210106.8

Repro Steps:

1. Make sure there is no folder or workspace opening in VS Code.
2. F1 -> Docker: Add Docker Compose Files to Workspace... -> Check the notification.

Actual:
There is only one "Open Folder" button in the notification.

Suggestion:
Add another "Open Workspace" button in the notification.

More Info:
This issue also reproduces when executing "Add Docker Files to Workspace..." command without workspace.

[bwateratmsft]

We intentionally decided to exclude the "Open Workspace" button. Users can still open a workspace, of course, but most of our features work better with just folders rather than workspaces (especially debugging, see #2327 for example).