Issue only with milestones input

Name: issue-only-with-milestones
Type: boolean
Default value: false

This input will let you process only the issues that are linked to at least one milestone.
This can be useful when you use the milestones for triage.

# ...
name: Stale
id: stale
uses: sonia-corporation/stale@latest
with:
  issue-only-with-milestones: true