ci: add schedule for trivy scans

[dklimpel]

Checklist

• [x] make test-all (UNIX) passes. CI will also test this
• [x] unit and/or integration tests are included (if applicable)
• [ ] documentation is changed or added (if applicable)

Description of change

A schedule task to scan latest container image (with latest tagged binary).

At the moment there is no latest image and this PR has to wait for next tagged version.

[aelsabbahy]

I'm thinking of cutting a release this weekend to address the open CVE, also thinking of getting one last release in before the Travis cutover.. in case we run into unexpected turbulence.

I assume this PR will have to wait until after the release?

[dklimpel]

I assume this PR will have to wait until after the release?

Yes.

also thinking of getting one last release in before the Travis cutover.. in case we run into unexpected turbulence

Sounds good.

[dklimpel]

There is a version tagged with latest to scan per schedule, now.

[aelsabbahy]

Awesome, thanks!