DRAFT: Adds partner selling workflow

Why is this change being made?

As we scale selling services with our channel partners, we need to ensure our processes include new partner-sourced opportunities. These changes need to be made before we announce to internal account teams and partner services sellers.

relates to https://gitlab.com/gitlab-com/customer-success/professional-services-group/ps-leadership-team/ps-practice-management/-/issues/162

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