Add "Number of items answered" metric in the overview table

### Is your feature request related to a problem?

When running the action on discussions, it would be nice to be able to see the "Number of items answered" metric in the overview table

### Describe the solution you'd like

If `discussion` is found in the `search_query` then count the number of discussions marked as answered and display the count in the markdown and json output.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Trace how search_query values are handled for discussions and where the overview table produces markdown and JSON output. Confirm how discussions marked as answered are represented, then verify that the new count appears in both outputs only for discussion searches.

Written by the indexing model from the issue text.