Make CoC Incident Core Team section clearer

[jpthiele]

During our read through of the Incident response guidelines in the instructor training earlier we noticed that the last part on Core Team members is a bit unclear.

This PR reworks that section by adding the definition of a PEO and splitting the implications for CI and PEO employees.

There are still some FIXMEs in the PR as it was unclear to me what exactly to write there as I don't know some of the things missing.