Add backing indices to kibana_system permissions for TI packages supporting IOC expiration

[kcreddy]

With earlier permissions #94506 that were added, we were able to successfully install the package manually from the Kibana UI and also execute the transform.
However, the system tests for ti* packages failing due to permission error on the source indices of the transform:

Error: error running package system tests: could not complete test run: could not add data stream config to policy: could not add package to policy; API status code = 403; response body = {"statusCode":403,"error":"Forbidden","message":"Error installing ti_recordedfuture 1.7.0: security_exception\n\tRoot causes:\n\t\tsecurity_exception: Cannot create transform [logs-ti_recordedfuture.latest_ioc-default-0.1.0] because user elastic/kibana lacks the required permissions [.ds-logs-ti_recordedfuture.threat-*:[read], logs-ti_recordedfuture_latest.threat-1.7.0:[]]"}

Adding backing indices directly using .ds- prefix into the existing privileges fixed the system tests locally.

This PR adds a .ds- prefix into the existing privileges for the source indices of ti* packages so that backing indices are directly given permissions.

[kcreddy]

Closing since the issue turned out to be CI version of Elasticsearch. The system tests are successful with original permissions itself.