Is your feature request related to a problem? Please describe.
I'm trying to implement something suggested in #6556
A sleep or some sort of pause to the update is a simple solution but has little to no flexibility.
I'm thinking on processing the potential headers some sites send to improve how many feeds can be updated in a given period of time.

Describe the solution you’d like
An event feed_after_actualize or simplepie_after_init which should allow me to get the headers of the request made to the feed.

Describe alternatives you’ve considered
Since the extension would already be using feed_before_actualize to cancel the update, also could be to manually call the feed's URL to process the headers in this event.

Additional context
None.