DEICH-6102 MARC21+Normarc mapping updates and fixes

All changes related to updated mapping, except for instrumentation.

Merge is requested so that testing of new mappings can be started ASAP.

The old mapping code can be enabled by legacy mapping feature toggle, defined as environment variable. Search sources can be enabled and disabled the same way, through environment variables. For details see related PR: DEICH-0000 - Moved mimir source enabled flags to env variables.

Blackbox tests can be used to verify that production functionality is still intact.

Closes DEICH-6102