Detect major dependency version bumps (#571)

As seen in #507 and #569, there is no guarantee for us that minor
dependency updates are actually minor updates for the dependent
application itself. The Chart version might be minor - and therefore
automatically merged when build is green - but the used Docker image
inside the Chart could still be a major version change.

To effectively prevent such automerge when the application major version
changes, there is now a test file that has the currently used major
versions hard-coded. In case of an actual major bump, this file has to
be adjusted.

Looking at `redis-cluster`, there might be several major Chart versions
with the same major application version.

This PR is related to #409 but does not fully resolve it.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/571
Reviewed-by: pat-s <pat-s@noreply.gitea.com>

Makefile

@@ -9,7 +9,7 @@ readme: prepare-environment
 
 .PHONY: unittests
 unittests:
-	helm unittest --strict -f 'unittests/**/*.yaml' ./
+	helm unittest --strict -f 'unittests/**/*.yaml' -f 'unittests/dependency-major-image-check.yaml' ./
 
 .PHONY: helm
 update-helm-dependencies: