Add Principal role responsibilities

Why is this change being made?

This is part of the exit criteria for the IC gearing workgroup, the effort regarding defining the principal role is tracked by #10214 (closed).

The principal engineer role is a new position between staff and distinguished, it is part of our enginering IC leadership career path.

With the introduction of this new role, we spend some time looking at our Staff+ roles searching for a clear progression path.

To make the discussion easier to handle, and avoid duplication of work, this merge request introduces only the new principal role, the complete rework for staff and distinguished will be part of a new merge request once we finalize the content of this one.

Our idea is to have a set of requirements that identifies areas of growth for the next level as well as the acquisition of new skills. As a general rule, we have requirements that are bound to the IC scope of influence, but there are also requirements outlining the horizontal nature of the IC leadership roles.

The following table provides some examples of those different axis, the full content can be previewed on the working document (internal only).

	Staff	Principal	Distinguished
Scope of influence	Solve technical problems of the highest scope, complexity, and ambiguity for your team	Solve technical problems of the highest scope, complexity, and ambiguity for your sub-department	Solve technical problems of the highest scope, complexity, and ambiguity for your department
Counterparts interactions	Expose their team's technology and organizational needs	Expose technology and organizational needs to their department counterparts	Build technology and organizational bridges to key organizational partners
Business impact	Leads significant project work for OKR level goals for the team	Ensures that OKR level goals are aligned across several teams in their sub-department	Aligns business needs with department requirements and works on setting technical vision for the team
Some requirements begin on more senior roles		Leads conversations to remove blockers and encourage collaboration across teams	Anticipates and communicates delays, and blockers before they require escalation

Job family approvals

Per approval flow for a job family

• Assign to @sloyd for approval.
• Assign to @edjdev for approval.
• Assign to @sytses for approval and at mention him at #job-family Slack with a link to this MR.
• Ping @gl-total-rewards for a benchmark proposal

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
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  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)