* Add OSSF Security Scoreboard Scan
This PR adds OSSF's Security Scoreboard Scan, to help tighten CoreDNS's security practice.
OSSF Scoreboard is recommended by GitHub. The result will show up in project's "Code Scanning Alerts" (together with existing CodeQL scan we already have).
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
