Show overloaded Postgres functions as distinct signatures in Studio API docs

Problem Studio API docs currently identify RPCs by function name and read one parameter schema from PostgREST's Swagger 2 document. When Postgres functions are overloaded, PostgREST exposes only one overload in that document ([PostgREST #1154]( so Studio cannot display or generate accurate snippets for the other signatures. RpcContent.tsx already carries a TODO for this limitation. For example, search(term text) and search(term text, limit_count integer) share /rpc/search, but the docs may show only one argument set. A user can copy a snippet for the wrong overload or never discover the other callable signature. Proposed Studio approach 1. Read exposed database functions from Studio's existing pg-meta/database metadata path, which returns every function OID, schema, argument mode, name, type, and default status. 2. Keep the PostgREST schema as the source for endpoint-level summary/description, but use database metadata as the source for overload signatures. 3. Give each …