Сalculate the generations' numbers for MARC record imported via Data Import

To prevent "Lost Changes" errors we must calculate gen nums for all MARC records.
When new Record is created in the mod-source-record-storage calculate the generation of the created record. Generation should be incremented in case a record with the same matchedId exists and the snapshot it is linked to is COMMITTED before the processing of the current one started.
Update schemas: Record - make matchedId required, Snapshot - add processingStarted field to track the datetime when the parsing of records started.