In general, rename:

- lfc_approximate_working_set_size to
- lfc_approximate_working_set_size_seconds

For the "main" metrics that are actually scraped and used internally,
the old one is just marked as deprecated.
For the "autoscaling" metrics, we're not currently using the old one, so
we can get away with just replacing it.

Also, for the user-visible metrics we'll only store & expose a few
different time windows, to avoid making the UI overly busy or bloating
our internal metrics storage.

But for the autoscaling-related scraper, we aren't storing the metrics,
and it's useful to be able to programmatically operate on the trendline
of how WSS increases (or doesn't!) window size. So there, we can just
output datapoints for each minute.

Part of neondatabase/autoscaling#872.
See also #7466.

This shouldn't actually be merged as part of this PR. It's just to make
the images easier to test on staging.