fix(CI): Snyk monitor images

[domsolutions]

Motivation

We want to be sent alerts from Snyk when our docker images are found to contain CVEs. We don't want to have to trigger a workflow manually to find this out.

Summary of changes

• when we release, build images and instruct Snyk to monitor images
• only monitor if a docker tag is set i.e. a new release

Checklist

• Added/updated unit tests
• Added/updated documentation
• Checked for typos in variable names, comments, etc.
• Added licences for new files

Testing