Set lock_timeout for some data deletion transactions

As these can cause deadlocks. This will probably cause errors, so some
retrying will need to be added.

guix-data-service/data-deletion.scm

@@ -212,6 +212,8 @@ WHERE id IN (
       conn
       'delete-revisions-from-branch)
 
+     (exec-query conn "SET LOCAL lock_timeout = '5s';")
+
      (delete-from-git-commits conn)
      (delete-jobs conn)
 
@@ -581,6 +583,8 @@ WHERE NOT EXISTS (
                           "
 SET CONSTRAINTS derivations_by_output_details_set_derivation_id_fkey DEFERRED")
 
+                         (exec-query conn "SET LOCAL lock_timeout = '5s';")
+
                          (maybe-delete-derivation conn
                                                   derivation-id))))))
                  derivations)))))