Provide a hook or event subscriber for modifying the current alert banners

[andybroomfield]

Provide a method for altering the alert banners that are displayed programmatically, not just through condition field.
This is to account for scenarios whereby

• Global banners might need to be suppressed (Having sections of the site that emulate a microsite eg. Fostering not wanting Council wide announcements are displayed. It's possible to use condition field to target pages and use the include or exclude options, but it is an either / or thing.
• Change the order of the banners so service specific ones are first
• Auto hide if several banners so pages don't fill with alerts.

My initial thinking would be either a hook or an event subscriber so this is then available for devs to create the appropriate custom module to meet their needs, interested in others thoughts.

[andybroomfield]

Whats the best name for the hook?
localgov_alert_banner_banner_alter?
Anything needed to provide to the hooks apart from the banners?
This will be run the point where currentBanners is called (currently in the block) though it might be desirable to pass some context.