Add outputs with results URL, number of issues etc.

It would be nice to have results not only in form of stdout but also github action outputs. It would make integration of fossa scan into a workflow easier (e.g. generating comment of a PR after a scan).

Start by inspecting the action entry point and its current handling of FOSSA scan output, then check how GitHub Action outputs are declared and consumed. Define the required result URL and issue-count values, and verify that later workflow steps can use them while stdout still works.

Written by the indexing model from the issue text.