Increase 'operations-per-run' for the stale action (#1985)

The default value of 30 is too low for the repository and the action
fails to process all issues and pull requests.

This change also modifies when the job is executed to avoid running it
at the same time than prometheus-operator/prometheus-operator and
experience quota issues with the GitHub API.

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

Signed-off-by: Simon Pasquier <spasquie@redhat.com>