- Changes GITLAB_USER_LOGIN to TF_USERNAME for consistency with TF_ADDRESS
- Changes GITLAB_TF_PASSWORD to TF_PASSWORD for consistency with TF_ADDRESS
- Supplies GITLAB_USER_LOGIN when TF_USERNAME is unset
- Supplies gitlab-ci-token/CI_JOB_TOKEN when TF_PASSWORD is unset

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/216854
Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/216785