Set node config action to append if it's not defined

[gayanSandamal]

Description

@joepavitt I did couple of testings on my local instance but I couldn't recreate it

Screen.Recording.2024-10-16.at.10.36.33.mov

But when I did the same on the dashboard demos instance I could recreate the scenario https://dashboard-demos-dev.flowfuse.cloud/dashboard/table-1

Assuming the root cause is with setting the default in ui_table.js I'm creating this PR and keeping as draft until I get this confirmed with @joepavitt

Related Issue(s)

#1407

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[joepavitt]

Code changes looked fine, but all table-based tests are failing

[gayanSandamal]

Code changes looked fine, but all table-based tests are failing

This has happened due to default action method "append". This is fixed with 63bea01

Ready for review