GHA: new workflow to submit scan to Coverity Scan service

GHA: new workflow to submit scan to Coverity Scan service

Not on every push due to submit limits.

Use caching to not submit a scan for the same git commit
twice. Since we have many days without pushes to master
this saves a lot of Github and Coverity resources.

v2:
 - add caching to not submit redundant scans

Change-Id: I302ccc82f9d5c43b58350bbbf7f16ad1c559248f
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230911110735.34491-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27001.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 607ae9b821665dadb6bd0a3ceb6288bda10d5e67)