Allow for setting any Postfix variables in the config file (both main.cf and master.cf)

[dgraziotin]

This is a followup from #74, which would be closed by #75 but it seems to be stalled since July 2020.

I'm working to a similar solution that allows to change options for main.cf and master.cf through environment variables.

This is the extract from README.md that explains the added features.

Custom postfix configuration

SMF allows to use environment variables to add or change lines to postfix main.cf and master.cf configuration files.

• SMF_POSTFIXMAIN_* variables will edit postfix main.cf entries.

  • Format: SMF_POSTFIXMAIN_option_name=value
  • Example: SMF_POSTFIXMAIN_soft_bounce=yes will call postconf -e soft_bounce=yes and add the option.

• SMF_POSTFIXMASTER_* variables will edit postfix master.cf.

  • Format: SMF_POSTFIXMASTER_service__name__type__parameter_name=value Please note the double underscore __ to differentiate service and type (which require a / as separation symbol) and the single underscore _ used only by parameter names.
  • Example: SMF_POSTFIXMASTER_submission__inet__smtpd__recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject will call postconf -P submission/inet/smtpd/recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject and add the option.