Add Domain (tenant) REST handler and DTO

Add REST API handler and shared DTO for Domain (tenant) CRUD management.

### DTO (common/dto/manager/domain/)
- types.py: DomainOrderField, OrderDirection
- request.py: CreateDomainRequest, UpdateDomainRequest, SearchDomainsRequest (filter/order/pagination), DeleteDomainRequest, PurgeDomainRequest
- response.py: DomainDTO, CreateDomainResponse, GetDomainResponse, SearchDomainsResponse, UpdateDomainResponse, DeleteDomainResponse, PurgeDomainResponse, PaginationInfo

### PathParam (manager/dto/domain_request.py)
- GetDomainPathParam(domain_name: str)

### Handler (manager/api/domain/)
- DomainAPIHandler class with create/get/search/update/delete/purge methods
- create_app() with routes:
- POST /admin/domains — create
- GET /admin/domains/{domain_name} — get
- POST /admin/domains/search — search
- PATCH /admin/domains/{domain_name} — update
- POST /admin/domains/delete — delete
- POST /admin/domains/purge — purge

### Adapter (manager/api/domain/adapter.py)
- DomainAdapter(BaseFilterAdapter) — convert_to_dto, build_updater, build_querier

### Reference
- GQL v2: manager/api/gql/domain_v2/ (query with filtering/pagination)
- V1 client: client/func/domain.py (6 GQL operations)
- Pattern: manager/api/notification/ (handler + adapter structure)

JIRA Issue: BA-4543