The MANDIANT_ACTIVE_BREACH_IOC, MANDIANT_FUSION_IOC, and OPEN_SOURCE_INTEL_IOC feeds are deprecated in favor of the GTI_IOC feed

## Deprecate Deprecated The `MANDIANT_ACTIVE_BREACH_IOC`, `MANDIANT_FUSION_IOC`, and `OPEN_SOURCE_INTEL_IOC` feeds are [deprecated](https://cloud.google.com/chronicle/docs/deprecations) in favor of the `GTI_IOC` feed. After March 18, 2027, we will be removing the `MANDIANT_ACTIVE_BREACH_IOC`, `MANDIANT_FUSION_IOC`, and `OPEN_SOURCE_INTEL_IOC` feeds. For more information on how to migrate, see [Migrate Mandiant legacy feeds to GTI](https://cloud.google.com/chronicle/docs/detection/ati-fusion-feed#migrateToGTI).