Re-add GPG configuration feature (#374)

This reverts d5ce1a47ea and therefore adds the GPG feature back into main.
As it is a breaking change, this PR now also contains the required upgrade notes.

Closes #107 again.

Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/374
Reviewed-by: pat-s <pat-s@noreply.gitea.io>
Reviewed-by: John Olheiser <john+gitea@jolheiser.com>

.drone.yml

@@ -23,6 +23,15 @@ steps:
   - helm dependency update
   - helm template --debug gitea-helm .
 
+- name: helm unittests
+  pull: always
+  image: alpine:3.17
+  commands:
+  - apk add --no-cache -X http://dl-cdn.alpinelinux.org/alpine/edge/testing make helm git bash
+  - helm plugin install https://github.com/heyhabito/helm-unittest
+  - helm dependency update
+  - make unittests
+
 - name: verify readme
   pull: always
   image: alpine:3.17