Add upgrade logic for nextcloud chart

charts/nextcloud/upgrade_info.json

@@ -0,0 +1 @@
+{"filename":  "ix_values.yaml", "keys": ["image"]}

charts/nextcloud/upgrade_strategy

@@ -0,0 +1,30 @@
+#!/usr/bin/python3
+import json
+import sys
+
+from pkg_resources import parse_version
+from pkg_resources.extern.packaging.version import Version
+
+
+def newer_mapping(image_tags):
+    key = list(image_tags.keys())[0]
+    if not image_tags[key]:
+        return {}
+
+    versions = [v for v in map(parse_version, image_tags[key]) if isinstance(v, Version) and not v.is_prerelease]
+    if not versions:
+        return {}
+
+    versions.sort()
+    version = str(versions[-1])
+    return {
+        'tags': {key: version},
+        'app_version': version,
+    }
+
+
+if __name__ == '__main__':
+    if len(sys.argv) != 2:
+        exit(1)
+
+    print(json.dumps(newer_mapping(json.loads(sys.argv[1]))))