[docs] log rotation: add expected unit for interval and filesize

What does this MR do?

This MR add in documentation the expected unit for log rotation configuration. According to Merge request diff expected unit are seconds and bytes.

Related issues

N/A

Author's checklist

• Ensure the branch name starts with docs- or ends with -docs, so only the docs-related CI jobs are included
• Consider taking the GitLab Technical Writing Fundamentals course
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