Use default section to simplify GitLab pipelines

Problem/Motivation

Currently we define default job settings and variables with YAML aliases. GitLab supports a default top level section where we can move some settings common to all jobs: https://docs.gitlab.com/ee/ci/yaml/#default

Steps to reproduce

Proposed resolution

Determine which settings can be moved to the default section in both the parent and child pipelines.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet