Add rocky linux OS identification

[hanserasmus]

I added the one line of code in the librenms-agent repository to correctly identify Rocky Linux. This PR is just for adding the icon/logo.

DO NOT DELETE THE UNDERLYING TEXT

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Testers

If you would like to test this pull request then please run: ./scripts/github-apply <pr_id>, i.e ./scripts/github-apply 5926
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[librenms-bot]

This pull request has been mentioned on LibreNMS Community. There might be relevant details there:

https://community.librenms.org/t/22-3-0-changelog/18403/1