Fix/43005 attachments copied on wp copy

[ulferts]

Moves copying of attachments into the copy services (for work packages and wiki) so that copying of attachments will be included whenever the service is used.

This will lead to attachments being copied e.g. when copying a work package using the "Copy to other project" menu item and by that fixes: https://community.openproject.org/wp/43005

TODO

• [x] Move copying attachments into the wp copy service
• [ ] Move copying attachments into the wiki copy service
• [ ] Ensure copying options for wp attachments and wiki attachments are still presented on the copy project form
• [ ] Rename project copy options as specified by https://community.openproject.org/work_packages/43909