[DOCS][Backport][9.0] Reference cleanup (#124720)
* Fix external URI images (#124350)
* [DOCS] Plugin management reference cleanup (#124578)
* add content to plugin management
* add content to Plugin Management
* Update docs/reference/elasticsearch-plugins/plugin-management.md
Co-authored-by: florent-leborgne <florent.leborgne@elastic.co>
* fix applies-to tag
* add ech to docset.yml
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Co-authored-by: florent-leborgne <florent.leborgne@elastic.co>
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Co-authored-by: florent-leborgne <florent.leborgne@elastic.co>
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