[8.x] [8.16] Adds entity store docs (backport #6053)

[mergify]

Contributes to #5836 by adding documentation for the new entity store feature.

Only adds ESS docs – the serverless release date is TBD.

Previews:

• Entity risk scoring requirements
• Asset criticality | View and assign asset criticality
• View and analyze risk score data | Entity Analytics dashboard
• Entity store
• Entity Analytics dashboard

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  This is an automatic backport of pull request [8.16] Adds entity store docs #6053 done by Mergify.

[github-actions]

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