Add MARC 534 $p and $e to Cocina mapping

[estanfor]

We are currently mapping 534 $t, but without $p and $e this can result in apparently duplicate listings under "Related items" on the purl page. See https://jirasul.stanford.edu/jira/browse/PURL-1499. (It looks like the 534 fields have since been removed from the record that this ticket is about.)

Note on timing: we may address the display of related items on purl as part of the upcoming Argo workcycle. Coming up with a display label based on $p could be part of this, and the first step would be to get the values into Cocina.

Arcadia noted in Jira that this change would require a local change to the MARC2MODS XSLT, which is something we've been trying to avoid. Alternatively, Arcadia could ask the MODS Editorial Committee to include it in the official XSLT, but this would take longer.