Iterates on the PSE role definition

[michaelnoonan]

The goal of this change is to improve the clarity of the description so that:

• It's easier for L5's and their managers to share understanding of the expectations of the role
• It's easier for L4's (potential L5's) to have a clearer understanding of what's required to progress to L5 (if they have the appetite)

Key changes

• Clarify the focus of a PSE is their group, then the rest of Octopus
• Clarify where we expect PSEs to be "t-shaped" (broad understanding versus deep understanding)
• Introduces some traits I've observed of the best PSEs
  • Identifying patterns of organisational dysfunction and advocating effectively for improvement
  • Championing operational excellence and learning from incidents
  • Working with peers in other departments, like support/sales/marketing, to help a frustrated customer or improve overall customer outcomes

Process

• [x] I took inspiration from the workshop we ran with Principal Engineers and Engineering Directors at the Principal Enginering onsite in April 2024: https://docs.google.com/document/d/1IU26CW0wuftc9gFaJbkTHVpTjxkslE4APO374XWaRHg/edit
• [x] I spent an afternoon reading and reflecting on the examples I've observed over the last 12 months at Octopus and added a first draft of those ideas. These mainly aligned with the Customer Success traits.
• [x] Feedback from @andrewabest
• [x] Feedback from Engineering Directors (@hogfish @Waldo000000 @cstrzadala Ziv Levi)
• [ ] Feedback from Principal Software Engineers
• [ ] Feedback from @colinbowern