Current onboarding templates do not follow new role names

As you all know, we are all now Support Engineers with different focuses (Solutions Support Focus and Application Support Focus), however, onboarding templates have not been updated. We still have:

1. Onboarding - GitLab.com Support Agent.md
2. Onboarding - GitLab.com Support Engineer.md
3. Onboarding - Self-managed Support Engineer.md
4. ZZZ-DEPRECATED - Premium support onboarding.md

Proposal is to:

• Remove ZZZ-DEPRECATED - Premium support onboarding.md
• Rename Onboarding - Self-managed Support Engineer.md to Onboarding - Support Engineer - Solution Support Focus.md
• Rename Onboarding - GitLab.com Support Engineer.md to Onboarding - Support Engineer - Application Support Focus.md
• Remove Onboarding - GitLab.com Support Agent.md

This has also been discussed in #support-managers Slack channel. Shout if you see issues related to this!