Merge duplicated publications

[eloiferrer]

Issue description: After inserting the arXiv id in zbMath publications, it is possible now to identify several duplicated publication items. See: https://tinyurl.com/272j99ec Just merging these items will result in most of the merged items having duplicated authors. These repeated authors will also have to be merged.

TODOS:

• [ ] Merge duplicated items (+ delete linked publication pages)
• [ ] Merge duplicated authors

Acceptance-Criteria

Checklist for this issue:

• [ ] Assignee has been set for this issue
• [ ] All fields of the issue have been filled
• [ ] Issue has been assigned to the main project
• [ ] Code was merged
• [ ] Feature branch has been deleted and issues were updated / closed
• [ ] Issue is tracked by an epic, or the label 'non-epic' is set to the issue.