cron job to build dockerized jenkins

[damccorm]

Test building jenkins on jenkins!

Specifically, we would want to test the docker build: https://github.com/apache/beam/blob/master/.test-infra/dockerized-jenkins/README.md#setup-using-provided-scripts

docker build -t beamjenkins .

to catch issues like BEAM-14262

Imported from Jira BEAM-14264. Original Jira may contain additional context.
Reported by: ibzib.