postfix: Encrypt relay password with age

Switching from Ansible Vault to age.

This value is encrypted with the following public key:

    age1hl8dfgh938092h32zuex7xnfmqer3peg5gl6d892aarsw0s6nptq5tysu9

roles/postfix/templates/sasl_passwd.j2

@@ -1,5 +1,5 @@
 {% if smtp.mode == 'relay' %}
 {% if smtp.auth|d('none') != 'none' and smtp.username is defined %}
-[{{ smtp.host }}]:{{ smtp.port|d(25) }}	{{ smtp.username }}:{{ smtp.password }}
+[{{ smtp.host }}]:{{ smtp.port|d(25) }}	{{ smtp.username }}:{{ smtp.password | decrypt }}
 {% endif %}
 {% endif %}