* docs: Add frame selection and clean copy details to snapshots docs
Document how Frigate selects the best frame for snapshots, explain the
difference between regular snapshots and clean copies, fix internal
links to use absolute paths, and highlight Frigate+ as the primary
reason to keep clean_copy enabled if regular snapshot is configured clean.
* revert - do not use the word event
* rm clean copy is only saved when `clean_copy` is enabled
* Simplified the Frame Selection section down to a single paragraph.
* rm note about snapshot file ext change from png to webp
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Co-authored-by: Kai Curry <kai@wjerk.com>
