Add bulk replace to registrar area

#662

doc/repp/v1/domain_contacts.md

@@ -0,0 +1,19 @@
+# Domain contacts
+
+## PATCH https://repp.internet.ee/v1/domains/contacts
+Replaces all domain contacts of the current registrar.
+
+### Example request
+```
+$ curl https://repp.internet.ee/v1/domains/contacts \
+   -X PATCH \
+   -u username:password \
+   -d predecessor=foo \
+   -d successor=bar
+```
+### Example response
+```
+{
+  "affected_domains": ["example.com", "example.org"]
+}
+```