[Fleet] added read and delete privilege

[juliaElastic]

Follow up after #100574

Added read and delete privilege to be able to read and delete the index in FTR tests.
Currently the lack of delete privilege is causing unrelated FTR tests to fail that are trying to delete indices: elastic/kibana#168435

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[elasticsearchmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[kc13greiner]

LGTM; metrics-- are part of Fleet's data indexes for which kibana_system should be allowed elevated privileges and this pattern is appropriately listed in the docs as a potential collision pattern.