Docs: Plugin install deprecation note (#115160)
* Placeholder
* Updated note
* Update docs/sources/administration/plugin-management/plugin-install.md
* Feedback
* Update docs/sources/administration/plugin-management/plugin-install.md
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(cherry picked from commit fdc84474ce)
Co-authored-by: Anna Urbiztondo <anna.urbiztondo@grafana.com>
Co-authored-by: David Harris <david.harris@grafana.com>