With upgrade to Alpine 3.13, support for `hash:` and `btree:` has
beenremoved from Alpine.
As such `hash:<file>` references do not work any more.
[Alpine](https://wiki.alpinelinux.org/wiki/Release_Notes_for_Alpine_3.13.0)
explains it like this:
> Oracle has changed the license of BDB to AGPL-3.0, making it unsuitable
> to link to packages with GPL-incompatible licenses. Since the old version
> is no longer maintained, the db package is now deprecated. Alpine Linux
> packages are being transitioned to alternatives or, where no alternatives
> exist, removed entirely.
This, unfortunately, will mean that the new version of `docker-postfix`
might not be backwards-compatible, if you're using your own postfix
configuration. Sorry. :-(
Private keys generated with `DKIM_AUTOGENERATE` were created with
the root account and as such were not readable by OpenDKIM.
This fix will reown the created files to the `opendkim` user.
While quite annoying behavour, this is the how `postconf` works.
If you tell it to comment out a command, it will add it to the config
even when the same command exists commented out in the config file.
This commit does a bit of sed and grep magic to find if the comment
already exists and if yes, then it does nothing.
