Add process.name.caseless to logs-system.* mapping

[mbudge]

Please can we add process.name.caseless to the logs-system.* so we can get security rules which use this field working?

elastic/detection-rules#3390

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[mbudge]

These rules require process.name.caseless in winlogbeat-, logs-windows. and logs-system.security*

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[w0rk3r]

Changes were incorporated in ECS: elastic/ecs#2341.

They will probably be in 8.16, as this is not blocking any work and is an enhancement, I closed #9850 and will wait for the ECS release to modify the related rules.