add dnsConfig value support (#329)

Description of the change

Add support for a new value: dnsConfig, to be passed to the statefulset pod template configuration.

Default is {}, and does not change anything from current default pod configuration.
Benefits

Ability to fix some issues encountered with Alpine-based docker images, which may break DNS resolving on some clusters.

In particular, this allows to lower the ndots value, which fixes DNS resolving of FQDNs.

dnsConfig:
  options:
    - name: ndots
      value: "1"

Also, with this setting, one can set other parameters to finely tune DNS configuration for Gitea pods, if needed:

https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pod-dns-config
Possible drawbacks

None.
Additional information

Some relevant links about the issue this setting allows to fix:

https://stackoverflow.com/questions/65181012/does-alpine-have-known-dns-issue-within-kubernetes

https://gitlab.alpinelinux.org/alpine/aports/-/issues/9017
Checklist

    Parameters are documented in the values.yaml and added to the README.md using readme-generator-for-helm

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/329
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Reviewed-by: luhahn <luhahn@noreply.gitea.io>
Co-authored-by: dek <dek@noreply.gitea.io>
Co-committed-by: dek <dek@noreply.gitea.io>

templates/gitea/statefulset.yaml

@@ -287,6 +287,10 @@ spec:
     {{- with .Values.tolerations }}
       tolerations:
         {{- toYaml . | nindent 8 }}
+    {{- end }}
+    {{- if .Values.dnsConfig }}
+      dnsConfig:
+        {{- toYaml .Values.dnsConfig | nindent 8 }}
     {{- end }}
       volumes:
         - name: init