[8.x](backport #4694) [Cases] New cases subfeature privileges

[mergify]

Description

Relates to elastic/kibana#194898

This PR updates https://www.elastic.co/guide/en/observability/master/grant-cases-access.html to align with the changes in elastic/security-docs#6288

Documentation sets edited in this PR

Check all that apply.

• Stateful (docs/en/observability/*)
• Serverless (docs/en/serverless/*)
• Integrations Developer Guide (docs/en/integrations/*)
• None of the above

Checklist

• Product/Engineering Review
• Writer Review

Follow-up tasks

N/A

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This is an automatic backport of pull request #4694 done by Mergify.

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[mergify]

This pull request has not been merged yet. Could you please review and merge it @lcawl? 🙏

[mergify]

This pull request has not been merged yet. Could you please review and merge it @lcawl? 🙏

[eedugon]

LGTM

[mergify]

This pull request has not been merged yet. Could you please review and merge it @lcawl? 🙏