[DOCS-13129] Update CCM Permissions

[rtrieu]

What does this PR do? What is the motivation?

This PR makes the Permissions section of CCM its own page:

• Adds a Permissions page to the left nav
• Spells out the exact capabilities for each permission
• Updates the Data Access Control section since the feature is now GA

Merge instructions

Merge readiness:

• Ready for merge

For Datadog employees:

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Additional notes

[mikecretzman]

approved with a couple minor suggestions

[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/rtrieu/ccm-permissions-update/cloud_cost_management/permissions

Modified Files

• https://docs-staging.datadoghq.com/rtrieu/ccm-permissions-update/cloud_cost_management/