Update Incubation playbook to determine how best to collaborate with UX

Why is this change being made?

This MR clarifies the collaboration between Incubation and UX.

• Incubation does not headcount availability for UX at this stage.
• For the interim, the Incubation team will have to work within existing design patterns as much as possible, and resolve issues that come up in the UX reviews. All MRs with user-facing changes gets a review from a designer. For SEGs, we treat them similarly to community contributions, in that we want the designer closest to the area to work with the SEG as they will be deeply versed in our existing product.
  • In some cases, the SEG focuses on new areas of the product that doesn't have a direct impact on current stage group experiences. In these cases, we utilize the GitLab Roulette automation to help assign a Product Designer to an MR for review. The automation occurs when adding the UX label to the MR.
• If an SEG would like a designer to review and provide feedback (at any phase--early ideations, wireframes, high fidelity mockups, and so on) they can reach out to the Product Design Manager of the stage group/area of the product it likely impacts. This can sometimes be a challenge to know what group but any Product Design Manager can help you get you in touch with the right designer.
• If the SEG have advance notice of when you may need a designer to provide a review, it's best to let the Product Design Manager know as early as possible for better planning. Product Designers have very limited capacity but want to help SEGs by giving design critique so we can meet the quality standards of the GitLab product.
• The designer won't be responsible for solving the customer problem or putting together design assets. That should remain with the SEG.

Author Checklist

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• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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