Add vulnerability-allowlist.yml with relevant list of muted vulnerability scan issues

Some time ago, GitLab added ability to exclude some CVE- issues from security report by adding them to the file vulnerability-allowlist.yml in the root of the project.

We use it in dockerimages repository, but it only mutes it there. All products, that uses our images as base image should have the same ability.

One option is simply put the file in this repo, under /template.

More complex approach - automatically fetch it from dockerimages before container scanning.