SKY-6124 Minor docs updates for experiment

[shelleywang]

Changes
Fixed a small bug with the management API endpoint for editing variants

Add clarification to variant payload for the Exp Management APIs

We want to add "View Project API Key" to the permissions matrix for experiment permissions

• It doesn't fit in with any of the other tables (maybe Environments?) so I added a new Other category

[vercel]

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[shelleywang]

@SpencerFleury am I able to merge this or because I don't have a Vercel seat, will it not deploy properly?

[SpencerFleury]

@shelleywang I can do it :)