Use CI_ACCESS_TOKEN instead of CI_JOB_TOKEN

What does this MR do?

Following up !45 (merged) which did not work.

This MR updates our .gitlab-ci.yml to use $CI_ACCESS_TOKEN over $CI_JOB_TOKEN.

Why are we doing this?

It seems that authentication to our registry is currently broken and we are no longer able to login with our current credentials.

Here what I did to solve this issue:

1. Created an access token for the registry
2. Added it as a new CI variable
3. Updated our .gitlab-ci.yml
4. Tested it locally and it worked 🎉

docker login -u $CI_REGISTRY_USER -p $CI_ACCESS_TOKEN $CI_REGISTRY
WARNING! Using --password via the CLI is insecure. Use --password-stdin.
Login Succeeded

This MR changes how to login to the register by leveraging $CI_ACCESS_TOKEN which seems cleaner.