This patch moves the dovecot config from the container build to the helm
chart which allows to use templating with values that are configured at
runtime. This should provide more flexibility and standardizes the
dovecot container further.

This patch configures postfix to reject incoming email from its own
domains this is an effort to fight phishing of emails from my own domain
claiming to be from postmaster or alike.

References:
https://superuser.com/questions/964958/make-postfix-reject-incoming-email-spoofed-as-from-my-own-domain

The helm-unittest upstream has switched back to the helm-unittest
organisation again. Therefore switching to a different image. With the
switch a few minor, but breaking changes have been introduced.

- Dropping helm v2 support
- adjustment of indentation
- enforcing jsonpath for selection

Reference:
https://github.com/helm-unittest/helm-unittest

With different traffic policies and alike, the shared loadbalancer
causes more problems than it resolves. The original reason was that both
remote addresses would point to the same address, but this is a
non-issue given it all runs through a remote anyway.

This patch switches the externalTrafficPolicy to `Local` for the
proxy-protocol enabled services, in order to skip kube-proxy when
connecting, this makes sure that proxy-protocol can actually function
and doesn't hit a node that would need to redirect traffic.

References:
https://metallb.org/usage/#layer2
https://github.com/kubernetes/kubernetes/issues/66607
https://github.com/digitalocean/digitalocean-cloud-controller-manager/pull/206

Due to a copy-paste mistake, dovecot was using the postfix replicaCount
for its own. This is obviously not intended and was fixed by this
commit, correcting the snapshot and adding obviously needed tests to
prevent such a mistake in the future.

This patch creates a PDB for postfix, if the setup is scaled to more
than 1 postfix replica. This way at least one postfix instance should
always be available and the MTA therefore HA.

Currently the dovecot backend is not yet HA, this should take place
later on.

Currently each update of the application version requires an update of
the snapshot, this is annoying and doesn't help the chart with anything.
Therefore this patch enforces a chart version for all snapshot tests and
also stablizes the config reload hash magic regarding versioning
changes.

This patch should enable the postfix setup in MoK to utilise the
proxy-protocol and therefore gather required IP information from
connecting clients.

It's implemented based on some documentation regard the topic and is
useful for reverse-proxy setups e.g. behind haproxy.

References:
https://www.haproxy.com/blog/efficient-smtp-relay-infrastructure-with-postfix-and-load-balancers/

This patch adds the common config reload annotation trick to the MoK
helm chart, which should make sure that new users are picked up
immediately.

References:
https://helm.sh/docs/howto/charts_tips_and_tricks/#automatically-roll-deployments

This patch adds the needed network policies to the helm chart. This
provides a reasonable base-line setup. Currently any customizations
regarding network access would require additional policies. These might
come in place later on.

Adding a new helm chart to deploy functional mail server on Kubernetes.
It's composed of postfix and dovecot so far and handles user management
using Kubernetes secrets.