Replace `creator` with `first_owner` in EE specs

What does this MR do and why?

We're moving towards Owner role being possible in Projects. Because multiple owners will be possible soon, we are phasing out owner. To that end, we are ensuring that we're tidying up any technical debt that might exist around owner.

This MR replaces project.creator with project.first_owner in specs. The usages to be replaced are ones where the creator was being used in the spec as they are probably the owner, but we want to be explicit about that.

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Related to #351064 (closed)