Allow users to control how many samples should display on the insight. This value should be 1 <= X <= MAX, where max is the site config defined here.

We should always render the most recent snapshot if available, in addition to the selected N points. (cc @Joelkw for opinion on this. It will probably look like an off by 1 error in the UI. Maybe we just include snapshots in N?)

Example branch

/cc @Joelkw @felixfbecker @vovakulikov