Bug 34677: Update to MARC21 relator terms list (Apr. 26, 2021 technical notice)

This patch adds missing relator codes/terms to the marc21_relatorterms.yaml file in accordance with the April 26, 2021 technical notice.

https://www.loc.gov/marc/relators/tn210426rel.html

To test:
1. Apply patch and restart
2. Go to Administration > Authorized values > RELTERMS
   --> New term should be there

Addition:
pad - Place of address

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

installer/data/mysql/en/optional/marc21_relatorterms.yml

@@ -726,6 +726,10 @@ tables:
           authorised_value: "own"
           lib: "Owner"
 
+        - category: "RELTERMS"
+          authorised_value: "pad"
+          lib: "Place of address"
+
         - category: "RELTERMS"
           authorised_value: "pan"
           lib: "Panelist"