Allow API routes to optionally run as background function

[colinwirt]

Allow API routes to optionally run as background function

[lindsaylevine]

@colinwirt ok, yes, we can do this! but i'll restrict it to api pages only. your original PR would've in theory allowed for any page type to run as a background function.

[lindsaylevine]

lol hello again colin! i thought i recognized your name 😸 (original ask for reference #127)

so you're imagining a file in pages/api named something like users-background.js ?

[colinwirt]

Yes, that's right @lindsaylevine -- in fact that's how I've deployed the long running endpoint for my proof of concept using a fork of this package: a route called /api/contact-us-background

Using TypeScript meant it was non-trivial to extract this as a js function without a webpack step, so my first thought was to allow the name to include the -background suffix.