New hook onRequestBegin()

[brillout]

Description

New hook called right after renderPage() (before routing). I.e. it would be the first hook called upon rendering a page.

Thanks to #1588, the hook could be used for the server- and/or client-side.

Use case: init the vue-query client.

@4350pChris let me know if this becomes urgent / a blocker I'll then implement it sooner rather than later. (AFAICT it should be quick to implement.)

Potential alternative: https://vike.dev/onBeforeRoute.