Customizable .gnupg folder location (#186)

The `HOME` path is not persistent when using the rootless image, so the
`.gnupg` folder isn't either. Since the chart always used `/data/...` as
mount point for storage of all kinds, it is a minimal impact to just
relocate the dynamic `$HOME/.gnupg` folder location to the persistent
`/data/git/.gnupg`. This is where the signing keys are stored when
running root based environments. Doing so will

 - allow migrations between both image variants
 - persist signing keys for rootless environments

Fixes: #155

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/186
Reviewed-by: luhahn <luhahn@noreply.gitea.io>
Reviewed-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: justusbunsi <justusbunsi@noreply.gitea.io>
Co-committed-by: justusbunsi <justusbunsi@noreply.gitea.io>

templates/gitea/statefulset.yaml

@@ -120,6 +120,10 @@ spec:
               value: /tmp/gitea
             - name: TMPDIR
               value: /tmp/gitea
+            {{- if .Values.signing.enabled }}
+            - name: GNUPGHOME
+              value: {{ .Values.signing.gpgHome }}
+            {{- end }}
             {{- if .Values.statefulset.env }}
             {{- toYaml .Values.statefulset.env | nindent 12 }}
             {{- end }}