Skip migrating records already existing in new CDS

[kpsherva]

Example:
original record:
https://repository.cern/records/ebvyr-s5y37
harvested back to old CDS via INSPIRE:
https://cds.cern.ch/record/2933342

• find a way to detect these records
• skip them migration time
• mint the legacy recid to ensure redirection works
• still mark them as "migrated"