fix: Ensure configs are sanitized for parsing (#3819)

* chore: Detect missing final newline in configs read

These lines will be not be processed by `read`, emit a warning to raise awareness.

* fix: Ensure parsed config has final newline appended (when possible)

This functionality was handled in `accounts.sh` via a similar sed command (that the linked references also offer).

`printf` is better for this, no shellcheck comment required either.

We additionally don't attempt to modify files that are read-only.

* fix: Ensure parsed configs have CRLF to LF corrected (where possible)

Likewise, this runtime fix was only covering two config files. It now applies to all callers of this method.

* fix: Sanitize `postfix-master.cf` via helper

This feature should have been using the helper to avoid user error from their config updates accidentally introducing subtle breakage implicitly (due to CRLF or missing final newline).

* tests: Add test cases for new helpers

* tests:  `rm` is redundant when using `BATS_TEST_TMPDIR`

This temporary directory is created and removed implicitly. Even after a test failure.

* chore: Remove old `postfix-virtual.cf` migration logic

This was introduced in 2018, there should be no one needing to rely on this anymore?

* tests: Remove comment on sed failure concern

* chore: Add entry to `CHANGELOG.md`

* Apply suggestions from code review

Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>

---------

Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>

test/helper/setup.bash

@@ -102,7 +102,6 @@ function _init_with_defaults() {
 
   # The config volume cannot be read-only as some data needs to be written at container startup
   #
-  # - two sed failures (unknown lines)
   # - dovecot-quotas.cf (setup-stack.sh:_setup_dovecot_quotas)
   # - postfix-aliases.cf (setup-stack.sh:_setup_postfix_aliases)
   # TODO: Check how many tests need write access. Consider using `docker create` + `docker cp` for easier cleanup.