fix(topology): preserve incident continuity and application identity across topology re-imports

[Prabal864]

What

Fixes #6731.

When importing or re-importing topology YAML, TopologiesService.clean_before_import deletes all existing TopologyApplication records for the tenant. On recreation, create_applications_by_tenant_id assigns brand new internal UUIDs to applications that do not specify explicit IDs in YAML.

Because topology incidents link to applications via Incident.incident_application == application.id, TopologyProcessor._get_application_based_incident fails to locate the active incident for the recreated application and creates a duplicate incident when subsequent alerts fire.

Fix

1. In TopologiesService.import_to_db, query existing application IDs by (tenant_id, name) before cleanup, and preserve the existing UUID for matching applications.
2. In TopologyProcessor._get_application_based_incident, if lookup by application.id misses, fall back to looking up an active non-deleted topology incident by application name (Application incident: {application.name}) and re-link incident.incident_application = application.id.

Testing

• Updated tests/test_topology.py::test_import_to_db to assert that application IDs remain stable across successive imports.
• Added test_get_application_based_incident_fallback_by_name to assert that an existing active incident created under a prior application UUID is found and reconnected to the new application ID.
• python -m py_compile passes cleanly on all changed files.

Checklist

• I have read the Contributing Guide
• If you've added code that should be tested, add tests.
• If you've changed APIs, update the documentation.
• Ensure the test suite passes.
• Make sure your code lints (black/isort)