[seaweedfs] fix seaweedfs migration (#1430)

Signed-off-by: Andrei Kvapil <kvapss@gmail.com>

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## What this PR does


### Release note

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```release-note
[]
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## Summary by CodeRabbit

- New Features
  - None
- Bug Fixes
- Prevented duplicate or incorrect chart version updates during
migrations.
- Avoided failures when configuration values are missing or not
correctly structured.
- Preserved existing volume settings (size and storage class) during
updates.
- Refactor
- Reorganized migration steps to validate and create parent
configuration before modifying nested fields.
- Made the migration process more defensive and order-aware for smoother
upgrades.
- Chores
- Improved migration scripts for reliability during version and
configuration updates.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

scripts/migrations/19

@@ -22,9 +22,15 @@ kubectl get helmreleases.helm.toolkit.fluxcd.io -A \
 
   # JSON Patch
   | [
-      { op:"add", path:"/spec/chart/spec/version", value:"0.7.0" },
+      (if $s.chart.spec.version? then
+         {op:"replace", path:"/spec/chart/spec/version", value:"0.7.0"}
+       else
+         {op:"add",     path:"/spec/chart/spec/version", value:"0.7.0"}
+       end),
 
-      (if ($v.volume? | type) != "object" then {op:"add", path:"/spec/values/volume", value:{}} else empty end),
+      (if ($v|type) != "object" then {op:"add", path:"/spec/values", value:{}} else empty end),
+
+      (if ($v.volume?|type) != "object" then {op:"add", path:"/spec/values/volume", value:{}} else empty end),
 
       (if $v.size?          then {op:"add", path:"/spec/values/volume/size",         value:$v.size}          else empty end),
       (if $v.storageClass?  then {op:"add", path:"/spec/values/volume/storageClass", value:$v.storageClass}  else empty end),