chore(Amavis): only add configuration to Postfix when enabled

[georglauterbach]

Description

Since I am running Rspamd nowadays, I noticed there still are ports open that belong to Amavis. This is because the Amavis configuration is a fixed part of Postfix's master.cf. I changed that. Now, the Amavis section is added when Amavis really is enabled.

I took the chance and added proper indentation to master.cf; hence the diff is a bit fuzzy. But, only the Amavis part was adjusted, the rest is just styling.

Type of change

• Improvement (non-breaking change that does improve existing functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[polarathene]

Not really sure about storing the config in /etc/amavis within the container, but otherwise no other concerns 👍

Might be worth doing similar for the other 3 additions we have, but these are all default and not configurable I think. pickup in particular is modifying the original pickup config.

If I get around to refactoring the relay feature support, it'd be taking a similar approach to this Amavis appending. So I'm a bit more swayed towards a common location in the container (/etc/dms/postfix/master.d?)

[georglauterbach]

I updated the file location inside the container (to /etc/dms/postfix/master.d/postfix-amavis.cf). Also adjusted the indentation.

[polarathene]

@georglauterbach I noticed this:

docker-mailserver/target/postfix/main.cf

Lines 88 to 89 in 9e9f802

	# Additional option for filtering
	content_filter = smtp-amavis:[127.0.0.1]:10024

It's removed if ENABLE_AMAVIS=0, but probably should be added instead if ENABLE_AMAVIS=1?:

docker-mailserver/target/scripts/startup/setup-stack.sh

Lines 73 to 82 in 9e9f802

	if [[ ${ENABLE_AMAVIS} -eq 1 ]]
	then
	_log 'debug' 'Setting up Amavis'
	cat /etc/dms/postfix/master.d/postfix-amavis.cf >>/etc/postfix/master.cf
	sed -i \
	"s|^#\$myhostname = \"mail.example.com\";|\$myhostname = \"${HOSTNAME}\";|" \
	/etc/amavis/conf.d/05-node_id
	else
	_log 'debug' "Removing Amavis from Postfix's configuration"
	sed -i 's|content_filter =.*|content_filter =|' /etc/postfix/main.cf