feat(policy)!: Add manager column to provider configuration for multi-instance support (#2601)

### Proposed Changes

This PR implements the provider configuration manager column enhancement
and includes a significant architecture improvement to eliminate code
duplication.

 Core Features

- ✅ Added manager column to provider_config table with composite unique
constraint (provider_name + manager)
- ✅ Database migration with backward compatibility (existingrecords
default to 'local' manager)
- ✅ Updated protobuf definitions to require manager field in API
requests
  - ✅ Enhanced SQL queries and audit logging to support manager field

  Key Benefits

1. Multiple Instance Support: Create multiple provider configs with same
name but different manager types
2. No Code Duplication: Trust system is single source of truth for
available managers
3. Automatic Discovery: Well-known configuration endpoint automatically
exposes registered trust key managers
4. Premium Integration: Custom managers integrate seamlessly via
existing WithTrustKeyManagerFactories pattern
5. Backward Compatibility: Existing providers automatically assigned
'local' manager type

  Technical Changes

  - Database: Added manager column with composite unique constraint
- API: Manager field now required in CreateProviderConfig, optional in
UpdateProviderConfig
- Service: Validates against RegistrationParams.KeyManagerFactories
instead of separate registry
- Well-known Config: Dynamically populated from trust key manager
factories
  - Tests: Updated to reflect new validation approach

  Usage for Custom Managers

  Premium builds can add custom managers using the existing
  pattern:
```go
  server.Start(
      server.WithTrustKeyManagerFactories(
          trust.NamedKeyManagerFactory{Name: "premium-hsm",
  Factory: hsmFactory},
          trust.NamedKeyManagerFactory{Name: "premium-vault",
  Factory: vaultFactory},
      ),
  )
```
### Checklist

- [ ] I have added or updated unit tests
- [ ] I have added or updated integration tests (if appropriate)
- [ ] I have added or updated documentation

### Testing Instructions

Author: strantalis