Implement 'latest' tag for docker and apptainer container images

[tomlunderwood]

In this PR I modify the CI/CD pipeline so that whenever a container image is published in the container registry for this repo, and the tag for the container image is of the form v*.*.* (where * are non-negative integers), the container image is additionally given the 'latest' tag. This is the case for both the docker and the apptainer images generated by the CI/CD pipeline.

Moreover, in this PR I have also activated security scans via the anchore-scan job in the CI/CD pipeline. This had been deactivated while the repository was private. However, now that the repo has recently been made public, the scans can be used. Note though that they will only run in the main branch, so no scans will run until this PR is merged.

Evidence that the pipeline can generate a 'latest' tag successfully can be found at:

• https://github.com/PSDI-UK/data-transfer-container/pkgs/container/data-transfer-container%2Fdata-transfer for the docker images
• https://github.com/PSDI-UK/data-transfer-container/pkgs/container/data-transfer-container%2Fdata-transfer-sif for the apptainer images

Note that in both cases the 'latest' tag can be seen to be in operation. However, in this case to generate the 'latest' tag I - for testing purposes - disabled the check that the tag has the form v*.*.*. (The job which generated the 'latest' tag here is https://github.com/PSDI-UK/data-transfer-container/actions/runs/14129397837/job/39585746845). When the PR is merged the pipeline will have the desired behaviour: 'latest' tags will only be generated for container images which have tags of the form v*.*.*.

This PR completes the part of https://stfc.atlassian.net/browse/PSDI-477 pertaining to the data-transfer-container repo.

[stuart-stfc]

LGTM