L&R Workflow - Adding instructions for replacing a Subscription purchase of the incorrect type.

Why is this change being made?

Presently the L&R workflows do not contain a method for resolving a situation where a customer has received a subscription of the incorrect type (for example, if they received a SaaS subscription instead of a Self-Managed one, or vice versa).

Resolution of this situation is not within control of Support, however it can be fixed by Sales Support (and so I've included steps for how to request Sales Support do this, and also a link to their workflow for this situation).

@gitlab-com/support/licensing-subscription - any thoughts, edge cases, or otherwise on these changes?

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