In setup/flavor, change DMARC rua and ruf email default settings

DMARC_RUA and DMARC_RUF defaults will reuse the value defined for POSTMASTER,
instead of 'admin' as previously

setup/flavors/compose/mailu.env

@@ -76,8 +76,8 @@ FETCHMAIL_DELAY={{ fetchmail_delay or '600' }}
 RECIPIENT_DELIMITER={{ recipient_delimiter or '+' }}
 
 # DMARC rua and ruf email
-DMARC_RUA={{ dmarc_rua or 'admin' }}
+DMARC_RUA={{ dmarc_rua or postmaster }}
-DMARC_RUF={{ dmarc_ruf or 'admin' }}
+DMARC_RUF={{ dmarc_ruf or postmaster }}
 
 # Welcome email, enable and set a topic and body if you wish to send welcome
 # emails to all users.

towncrier/newsfragments/1463.bugfix

@@ -0,0 +1 @@
+Defining POSTMASTER through setup tool apply also to DMARC_RUA and DMARC_RUF settings