JQ helpers: support for includedNamespaces

We allow to exclude namespaces via an option, but sometimes it's desirable to generate a small and known subset of signals.

JQ filter that implements it is not trivial (nothing in JQ is), so it might be a good idea to support includedNamespaces and support filtering in this way as well.

Here's the filter

    filter: >
      semconv_grouped_metrics({"exclude_deprecated": true})
      | map(.metrics)
      | flatten
      | .[]
      | select (($included_namespaces | length == 0) or (.root_namespace as $ns | $included_namespaces | index($ns)))

The issue names no file or test. Start by locating the existing namespace-exclusion option and its JQ filter, then compare it with the provided includedNamespaces filter. Done means the option selects the requested root namespaces, preserves the empty-list behavior shown, and is covered by relevant tests.