Define `tags:` globally for all jobs

What does this MR do?

Instead of defining tags: per-job, we can use default:tags: to clearly indicate that all jobs use tags:

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/210457

Related to: https://gitlab.com/gitlab-org/gitlab/-/issues/210571

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides