AH00558: apache2: Could not reliably determine the server's fully qualified domain name

Describe the bug
After applying the helm chart I see the following error in the logs:

$ kubectl logs -n nextcloud nextcloud-7bd4647bbf-kc4wp -f
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 10.244.0.125. Set the 'ServerN                                         ame' directive globally to suppress this message
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 10.244.0.125. Set the 'ServerN                                         ame' directive globally to suppress this message

Version of Helm and Kubernetes:

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"21", GitVersion:"v1.21.0", GitCommit:"cb303e613a121a29364f75cc67d3d580833a7479", GitTreeState:"clean", BuildDate:"2021-04-08T16:31:21Z", GoVersion:"go1.16.1", Compiler:"gc", Platform:"linux/arm64"}
Server Version: version.Info{Major:"1", Minor:"21", GitVersion:"v1.21.0", GitCommit:"cb303e613a121a29364f75cc67d3d580833a7479", GitTreeState:"clean", BuildDate:"2021-04-08T16:25:06Z", GoVersion:"go1.16.1", Compiler:"gc", Platform:"linux/arm64"}

$ helm version
version.BuildInfo{Version:"v3.5.3", GitCommit:"041ce5a2c17a58be0fcd5f5e16fb3e7e95fea622", GitTreeState:"dirty", GoVersion:"go1.15.8"}

Which chart:
nextcloud:2.6.1

What happened:
The error AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 10.244.0.125. occurs.

What you expected to happen:
normal startup of nextcloud without an error message

How to reproduce it (as minimally and precisely as possible):
apply the helm chart

Anything else we need to know:
As a workaround I can add the following lines of code to my values.yaml file:

lifecycle:
  postStartCommand: ["/bin/sh", "-c", "echo \"ServerName 172.16.4.35\" | tee -a /etc/apache2/apache2.conf"]

But this is not how I expect that it should work like.

Start by inspecting the chart templates and the values.yaml lifecycle.postStartCommand workaround, then review the issue's comment thread for the intended configuration path. Done means a normal Helm deployment no longer emits AH00558 without requiring that workaround; validate with kubectl logs.