[Update] Approve "Missing Scene Performers"

[AdultSun]

Needs official approval: https://guidelines.stashdb.org/docs/scenes/scene-performers/#missing-scene-performers

This one gets pushback from newer contributors, but it doesn't actually say, "Downvote any scenes missing listed male performers." It says they "should be included" if they're listed and that finding missing names from external sources (IAFD, etc.) is "greatly encouraged, but often not required." I don't expect the core of the language to be modified here but there will likely be suggestions to strengthen or weaken the guideline's recommendations on how to enforce it.