CI, CIAO: add schedule pipeline to build docker images

What

A scheduled pipeline to re-build docker runtime image regularly

Why

Re-building docker images regularly should help fixing and avoid having severe vulnerabilities in our base docker images

How

So forcing re-building docker images will enforce the install of the last available Alpine packages (that tends to have the last healthy packages - packages without vulnerabilities -)

Manually testing the MR

You can run the pipeline using scheduled.sh script: TZ_SCHEDULE_KIND=DOCKER_FRESH_IMAGE_BUILD ./scheduled.sh What to look for:

• The pipeline starts without any issues
• The different steps should always enforce the build of the docker images (i.e. example )
• All the pipelines have passed successfully

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR