docs: make `matchData` use cases more discoverable

[mtardy]

One idea would be to add some kind of notes around the existing selectors, saying that you can extend those by using the generic matchData https://tetragon.io/docs/concepts/tracing-policy/selectors/#data-filter.

And provide more examples in matchData like the one reproducing matchUID.

I found a solution following #1943 (comment)

It works properly with

data:
- type: "int"
  index: 0
  source: "current_task"
  resolve: "cred.uid.val"
selectors:
  matchData:
  - index: 0
    operator: "GreaterThan"
    values:
      - "1000"

I hope it could help I hope this can help someone looking for the same thing as us.

I close the issue. Regards.

great! :)

Originally posted by @mtardy in #4455