Bug 36515: Amend MARC modification templates so control fields can be copied to subfields

Bug 36515: Amend MARC modification templates so control fields can be copied to subfields

Test plan:
1. Apply patch and restart services
2. Create a MARC modification template with the action:
 Copy and replace field 001 to 099$a unless 099$a exists
3. Perform a Batch record modification using your MARC modification template from #2
4. Confirm that the template has successfully moved the 001 control field value to the 099$a subfield

Sponsored-by: Education Services Australia SCIS
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>