Allow to set custom Cache-Control header for custom error

[mykolasmolis]

Goals

1. To be able to cache the custom error page

Non-Goals

No response

Background

When using customer errors (https://nextjs.org/docs/pages/building-your-application/routing/custom-error) there is a desire to be able to cache the response for some time. To reduce the load for functionality that is down for that moment. For example to cache the response on CDN by responding with custom Cache-Control header.

Proposal

To support getServerSideProps on custom error pages in order to be able to set custom headers.