Add an API to support speculation rules

Problem/Motivation

The speculation rules API is a structured way of telling the browser about links and assets it should prefetch

https://developer.mozilla.org/en-US/docs/Web/API/Speculation_Rules_API

We should add an API to support it

Steps to reproduce

Proposed resolution

Decide how we can make use of this
Design an API
Implement it

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet