docs: add incident management and postmortem docs

[monotykamary]

What's this PR do?

• [x] Adds details on incident management
• [x] Adds the 5 Whys technique to use for postmortems
• [x] Adds basic template outline for postmortems based on Atlassian work

[monotykamary]

@monotykamary just a small comment on the format Response, Recovery, Timeline, and Root cause identification should be formatted as h2 right 🤔

My bad, they should be H3 as they are child topics of postmortems.