paperless-ngx: an empty barcodes block falls back to the chart defaults

A "barcodes:" key left without children (e.g. after deleting the last
remaining sub-key, PAPERLESS_CONSUMER_BARCODE_SCANNER, which paperless-ngx
3.0 removed) is YAML null and replaced the whole default sub-tree on merge.
Rendering then failed on the nil pointer, so the release simply stopped
updating.

An empty or null block now means "the chart defaults apply". The merge runs
through a new paperless-ngx.defaultedDict helper: nulls never delete, nested
maps merge recursively, and explicitly set values win - including false and 0,
which "default" and "mergeOverwrite" would swallow. A scalar where the
defaults define a map is rejected with the values path in the message.

Major bump: the meaning of a values override changes.

Fixes #61

paperless-ngx/Chart.yaml

@@ -5,7 +5,7 @@ icon: https://raw.githubusercontent.com/paperless-ngx/paperless-ngx/dev/src-ui/s
 
 type: application
 
-version: 10.0.0+up3.0.5
+version: 11.0.0+up3.0.5
 
 appVersion: 3.0.5