[Docs] Add link to permissions for reporting features

[florent-leborgne]

This PR adds a small section at the top of the reporting and sharing usage docs to mention permissions, with a link to the detailed page.

This will be for all versions since 8.6, and I'll make sure it's added to the new markdown docs (v9) as well.

Request: https://elastic.slack.com/archives/C0JF80CJZ/p1739357256988339

Preview of the change:

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Pinging @elastic/kibana-docs (Team:Docs)

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[github-actions]

Warning

It looks like this PR modifies one or more .asciidoc files. These files are being migrated to Markdown, and any changes merged now will be lost. See the migration guide for details.

[github-actions]

Warning

It looks like this PR modifies one or more .asciidoc files. These files are being migrated to Markdown, and any changes merged now will be lost. See the migration guide for details.

[florent-leborgne]

Closing as asciidoc files are about to be removed from the main branch. This change has been done in the new docs in /docs-content