* forwarding: add a warning for public ports
A number of users have raised some security concerns about port
forwarding. Forwarded ports are private (requiring auth with the same
GH account that did the forwarding) by default. When making a port
public, show the following dialog:

* Update extensions/tunnel-forwarding/src/extension.ts
Co-authored-by: Joyce Er <joyce.er@microsoft.com>
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Co-authored-by: Joyce Er <joyce.er@microsoft.com>