Add project-level app config GraphQL query

## Description

Implement GraphQL query to retrieve app configuration at the project level with domain inheritance support.

## Tasks

- Define project-level app config schema
- Implement query resolver with domain inheritance logic
- Add permission checks
- Write tests including inheritance scenarios

## Acceptance Criteria

- Project-level app config can be queried via GraphQL
- Domain config inheritance works correctly
- Proper access control is enforced
- Tests verify functionality and inheritance

JIRA Issue: BA-4123