dynamic filter negate option

[Bullenj01]

@sebastien-coavoux and others I was reading your pull request for dynamic filters and thank you for implementing that. Without it I don't think I would have been able to go to production with this stack. I've been working on a networking centric observability and alerting platform. When you are ingesting routers and switches anything involving interfaces can really cause your metric count to balloon. For example, I'm working on env monitors right now using the Entity-state-mib. if I pull entStateOper with no filters I pull a few sensors from each interface. I'm currently collecting information on around 12000 interfaces so that adds up. Most of those turn out to be junk metrics as well cause the sensors on these generic fiber modules do not seem to work well with the vendors threshold readings. What would be nice is a negative regex filter. Ideally in the config file under filters you'd have something like:

notvalues:
  - ^DOM.*$
  - ^.*Ethernet.+
values:
  - ^Power.*$

The reason for a negative regex is because a positive regex match on everything else is pretty hacky and time consuming. There are alot of other sensor types on each device that I want to collect.
I did try a pure regex solution of using negative look aheads but found, after some trial and error, that golang does not support negative lookaheads so I think these may have to be some kind of set operation in your filterAllowedIndices function. And I should mention I can get what I want after the fact by using a metric_relabel to drop the DOM stats but that is after the scrape and also it would be nice to have all snmp functionality contained within the exporter. Any thoughts on if this is viable and worth the squeeze?