Document current SIMP CI/CD/RELENG process and procedures

There have been many changes within SIMP's CI/CD/RELENG processes in the last few months.

It is now complex and codified enough that contributors should have documentation to better understand and maintain it.

Among the topics that should be covered:

• RELENG automation

• Travis CI pipelines

  • ENV variables

  • Common use cases

  • Updating (puppetsync)

• GitLab CI pipelines

  • ENV variables

  • Updating (puppetsync)

  • Scheduled jobs

  • Common use cases

• Common Asset Syncs

  • What is managed and why

  • How to manage a comment asset push

  • Guidelines (what to manage or not, how to handle approvals, testing)

  • Common use cases

  • Updating (puppetsync)

• RELENG misc topics

  • GitHub CI maintenance

  • GitLab CI maintenance