Skip integration dashboards in dashboard lists

[riyazsh]

Summary

• drop integration-owned dashboards from manual dashboard-list membership before sync diff/apply
• keep custom dashboard remapping unchanged
• defensively filter integration dashboards from the final dashboard-list membership update payload

Why

Manual dashboard lists can contain integration dashboards/timeboards. Those IDs are org-local and are not replicated as custom dashboards, so sending them to the destination list-membership API can fail with 404 when the corresponding integration dashboard does not exist in the destination org.

Testing

• tox -e py -- --black datadog_sync/model/dashboard_lists.py tests/unit/test_dashboard_lists.py