Add AlsoTo downstream failure propagation support

[Arkatufus]

Fixes #7269

Changes

Add some new API for AlsoTo that allows users to opt-in to propagate downstream failures to its parent stream. If any flow/stage failed downstream of the AlsoTo flow, it will also cancel the parent stream with the same cause.

The default behavior will still ignore any cancellation/failures from downstream stages/flows

[Aaronontheweb]

I would probably make this enabled by default - since that's what I'd expect if I were an end-user.

[Arkatufus]

That would be a breaking change for existing implementation

Talked to Aaron about this offline, we decide that the correct behavior should be the default, even when it is a breaking change.

After some deliberation, the old behavior actually have a purpose, we're keeping the old behavior.

[Arkatufus]

Done, failure propagation is the default behavior now