docs: document GraphQL select option for field projection

[MHJahanbakhsh]

Description

Documents the GraphQL select boolean argument introduced in #13711 so users know how to enable database-level field projection from GraphQL queries.

• Add a Select section to the GraphQL overview with an example
• Add a GraphQL API section to the Select docs explaining that select: true derives the projection from the selection set
• Mention Select (including GraphQL select: true) on the Performance overview under querying guidance

Fixes #14465

Testing

• Docs match GraphQL resolver behavior (select?: boolean + selection-set projection)
• Examples align with existing Local/REST Select docs and GraphQL tests