Currently master.cf only allows for _very_ limited configuration
options mainly focussed on SMTP submission settings.
This is rather limited and does not scale very well for managing
the other services defined in master.cf.
This patch has moved all the service definitions into a jinja file
and generates the master.cf service definition on the fly based on
these defaults.
Defaults can be overridden in a pillar to customize the rendered
master.cf file accordingly to local needs.
Undefined values will be filled with the postfix defaults.
Care has been taken that the previous ways of managing the submission
configuration options are still supported for backwards compatibility
to prevent breakage for existing users of the formula.
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