Add player admin API docs

[tudddorrr]

Player admin API reference

• Added a new player-api page documenting how to search for players, read them, and update their props or delete them server-side.
• Documented the Player, PlayerAlias, Prop and RejectedProp types, including the reasons a prop can be rejected.
• Registered the page in the Admin API reference navigation.

Bruno collection

• Extended the collection's Admin API folder with the player admin requests so the API reference and the collection stay in sync.
• Updated the collection documentation to list Players alongside Game config, Leaderboards and Stats.

Bruno collection export

• Regenerated the published bruno-collection.html export to include the player admin requests and refreshed metadata.