Support recursiveness in file eventsource

[AmitMendl]

Is your feature request related to a problem? Please describe.
working with the file eventsource feels limiting since it cannot look recuresively inside a folder (i.e. folders inside folders)

Describe the solution you'd like
An option to enable resursiveness on the file eventsource

Describe alternatives you've considered
My current workaround is to write a recursive watcher that trigger a webhook eventsource

Additional context
I'd want to help contribute to this feature.
by default this option should probably be false so that the behaviour of the eventsource will be backward compatible.

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