gotenberg: null-safe hardening, probes and resources

Retrofit of #99 for a chart that already carries a values.schema.json,
plus the schema type change that goes with it.

An override written without children is YAML null. Where the chart
defines a default, Helm's coalescing deletes the default before schema
validation runs, so the schema never sees the null and cannot reject it:
the container rendered "securityContext: null" - unhardened, healthy,
silent. Where the chart defines no default (resources.limits), the null
survives into validation and a strict "object" type aborted the render.

The defaultedDict helper from #96 handles the first case; widening the
types of exactly these blocks to ["object", "null"] handles the second.
All other keys stay strict, additionalProperties: false is untouched.

The probes address the container port by name, so a rebuilt default probe
needs no further context.

Rendering with normal values is byte-identical to 5.0.0.

gotenberg/Chart.yaml

@@ -5,7 +5,7 @@ icon: https://gotenberg.dev/img/logo.png
 
 type: application
 
-version: 5.1.0+up8.36.0
+version: 6.0.0+up8.36.0
 appVersion: "8.36.0"
 
 maintainers: