Refactor container settings in values.yaml for clarity

The structure of the container options in the `values.yaml` file has been
modified to improve clarity and organization. The `defaultContainerOptions`
section has been replaced with a `containers` section containing a
`main` container. This change enhances readability and aligns with common
best practices for defining container settings in Helm charts.

No breaking changes were introduced, and the default image repository
and tag remain unchanged. This refactor aims to streamline the
configuration process for users.

charts/paperless-ngx/values.yaml

@@ -7,7 +7,8 @@
 controllers:
   main:
     type: deployment
-    defaultContainerOptions:
+    containers:
+      main:
         image:
           # -- Image repository
           repository: ghcr.io/paperless-ngx/paperless-ngx
@@ -19,6 +20,7 @@ controllers:
           # @default -- See [values.yaml](./values.yaml)
           # -- Set the resource requests / limits for the container.
           resources: {}
+
 env:
   # -- Set the container timezone
   TZ: UTC