Reload dashboard when Stats API version changes

[macobo]

Idea from the lovely @apata for making easier breaking changes in the dashboard API: reload the dashboard when the internal API version changes.

This will help us make 'breaking' changes easier.

[apata]

In my mind, this risks us creating an endless reload loop for all dashboards when we fail to keep things in sync. There's a small chance of that happening, but the damage would be great.

I think we could mitigate it by instead doing window.location.replace, adding the r=... query parameter with value of EXPECTED_API_VERSION, like r=5.

Then, in this function, we can make the reload conditional on query not containing r=${EXPECTED_API_VERSION}.

There's a decent example of something similar in url-search-params.ts: perhaps this logic could be colocated there?

[apata]

Having it in the JSON payload is good: it catches the eye when refactoring the payloads server side. But, it also misses a few routes that the dashboard is using, like sites, segments, funnels.

Did you consider providing it in a header?

It seems to me that if it were a header, we could provide it with a router plug on all those APIs and use it as the definitive trigger for reloading incompatible dashboards.