add dmarc dns record support to the dns plugin

Descriptive title for this enhancement

add dmarc dns record support to the dns plugin

Actual behavior

we don't know if argonaut support correctly the dmarc dns record

Expected behavior

to ba able to generated dmarc record from ldap for bind

Benefits

be able to manage dns records with FusionDirectory & argonaut-ldap2zone

Possible Drawbacks

none