Attachment Right/Left Filler

Feature Request: Attachment Fillers for New Library

This feature request introduces a feature for filler attachments, specifically for the left and right sides.
The functionality mirrors a previous feature request called "Attachment Left Side."
The new feature (Attachment Left Filler, Attachment Right Filler) allows users to select filler attachment screw holes if a filler will be applied on the left side or the right side.
The new library will eventually incorporate these features, but they are not available yet, necessitating this request.
Verify that selecting "Attachment Left Filler" correctly unchecks "Attachment Left Side" and adds three countersunk holes on the left side.
Ensure that selecting "Attachment Right Filler" functions similarly, adding countersunk holes on the right side.
Test the integration with the new library to confirm that existing customizations remain intact after updates.