feat: new methods to return destination instance id and client id for agw

[NicoleMGomes]

Disclaimer: Do not include SAP-internal or customer-specific information in this PR (e.g. internal system URLs, customer names, tenant IDs, or confidential configurations). This is a public repository.

Description

Adds two new public methods and supporting infrastructure for resolving runtime identity credentials:

• DestinationClient.get_service_instance_id(): reads the destination service instance ID from mounted secrets via the standard mount/env-var fallback resolver. Raises DestinationOperationError on failure.
• AgentGatewayClient.get_ias_client_id(): returns the IAS client ID, auto-detecting agent type (Customer vs LoB). Customer agents read client_id from the mounted credentials file; LoB agents fetch the sap-managed-runtime-ias-{landscape} destination at provider subaccount level using the new skip_token_retrieval option. Raises AgentGatewaySDKError on failure.
• ConsumptionOptions.skip_token_retrieval: new field that passes $skipTokenRetrieval=true to the Destination Service v2 API, skipping OAuth2 token exchange when only destination properties are needed.

Both methods are instrumented with telemetry (record_metrics) and covered by unit and integration tests.

Related Issue

Closes #

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Dependency update

How to Test

1. Unit tests: uv run pytest tests/destination/unit/test_client.py::TestGetServiceInstanceId tests/agentgateway/unit/test_agw_client.py::TestGetIasClientId tests/agentgateway/unit/test_lob.py::TestGetIasClientIdLob -v
2. For get_service_instance_id: set CLOUD_SDK_CFG_DESTINATION_DEFAULT_INSTANCEID=<your-id> and call DestinationClient(...).get_service_instance_id() — expect the value back; unset the env var and call again — expect DestinationOperationError.
3. For get_ias_client_id (LoB): with a bound destination service and APPFND_CONHOS_LANDSCAPE set, call AgentGatewayClient(tenant_subdomain="...").get_ias_client_id() — expect the IAS clientId from the sap-managed-runtime-ias-{landscape} destination.
4. For get_ias_client_id (Customer): with a credentials file mounted at the standard path, call AgentGatewayClient().get_ias_client_id() — expect client_id from the credentials file.
5. Integration tests (requires BTP binding): uv run pytest tests/destination/integration/ tests/agentgateway/integration/ -k "instance_id or ias_client_id"

Checklist

• I have read the Contributing Guidelines
• I have verified that my changes solve the issue
• I have added/updated automated tests to cover my changes
• All tests pass locally
• I have verified that my code follows the Code Guidelines
• I have updated documentation (if applicable)
• I have added type hints for all public APIs
• My code does not contain sensitive information (credentials, tokens, etc.)
• I have followed Conventional Commits for commit messages

Additional Notes

The skip_token_retrieval option is used internally by the LoB flow of get_ias_client_id() to avoid an unnecessary OAuth2 token exchange when fetching the IAS destination — only the destination properties (clientId) are needed. The $skipTokenRetrieval query parameter is a supported Destination Service v2 API feature.