linked-records: improve search query

[zzacharo]

Example: https://repository.cern/records/xjyz5-s8d31
Query generation function: https://github.com/CERNDocumentServer/cds-rdm/blob/master/site/cds_rdm/views.py#L67

• The query that retrieves records referencing the current record appears to only consider the internal record ID. However, references may also use identifiers (e.g. schemes CDS, DOI, CDS reference number(?)).
• When querying for linked records based on the related identifiers, consider taking into account also other schemes than CDS e.g DOI, CDS reference number