Add spec pr template

[felixbarny]

• Adds a pr template for agent specs.
• Removes process-spec.md in favor of more concise PR template checklist. This is debatable but parts of the process is outdated and it's a bit TL;DR. Seems easier to only have one single source of truth. If important details are missing in the pr template, we can add them as comments.
• Adds a more lightweight process for smaller enhancements/fixes.
• Adds a checkbox for dealing with sensitive info.

This is a small enhancement

• [x] Create PR as draft
• [x] Approval by at least one other agent
• [x] Mark as Ready for Review (automatically requests reviews from all agents and PM via CODEOWNERS)
  • Remove PM from reviewers if impact on product is negligible
  • Remove agents from reviewers if the change is not relevant for them
• [ ] Merge after 2 business days passed without objections

[apmmachine]

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#### Build stats * Start Time: 2021-11-15T10:10:59.257+0000 * Duration: 3 min 13 sec * Commit: c57f3a0716ec56ad6dd50039ce781982fde45e56

[felixbarny]

In accordance to the PR template, I'll merge this tomorrow 5:30pm CET if there are no objections.