insights: allow users to filter out captured values in a detect and track insight

Created by: coury-clark

When we generate dynamic series from a capture group insight (detect and track) we can get an arbitrary list of results, for example:

green: 3
blue: 7
orange: 50
transparent: 4

In some cases, we want to exclude matches but cannot do so directly in the regexp without negative lookaheads (which are not supported and are likely not coming). We can consider doing this in a post-hoc filter, allowing users to specify excluded capture values and filter them out at request time.

Here is an example on a hack branch from a few months ago.