Added image tags for major versions

[simonjamain]

Resolves #525

• [ ? ] Bugfix (non-breaking change which fixes an issue)
• [ ? ] New feature (non-breaking change which adds functionality)

Proposed changes

see #525 for the origin

The introduction of a new registry tag holding only the major version (keeping and ofc) to allow easy tracking of major changes only.

Examples of images with this principle :

nginx : https://hub.docker.com/layers/library/nginx/1
traefik : https://hub.docker.com/layers/library/traefik/3

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team. (not really, discussed here No registry image tag for major versions #525)
• I have run grunt to verify the unit tests pass (N/A, I don't think that any tests are covering those tags)
• I have added suitable unit tests to cover the new/changed functionality (N/A, I don't think that any tests are covering those tags)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: simonjamain / name: simonjamain (baa8dbd)

[hardillb]

I'll look at this later, it may be the weekend