RLS to support multi-tenancy

[ankitsejwal]

Requirement: Pgweb must read user role from HTTP header X-Database-Role
Behavior: When header is present, automatically execute SET ROLE {role_name} before every database query
Scope: Applies to ALL database operations (queries, schema browsing, metadata calls)

Universal Query Wrapping:

• Inject SET ROLE for all database operations

Graceful Degradation:

• Requirement: When X-Database-Role header is absent, pgweb operates normally
• Behavior: No SET ROLE injection, uses default connection credentials
• Purpose: Maintains backward compatibility