## Description
<ins>Problem</ins>
The action configuration UI lacked support for running actions
specifically on page unload, limiting automation and flexibility for
users.
<ins>Root cause</ins>
There was no ON_PAGE_UNLOAD option in the ActionRunBehaviour enum or
related UI, and feature flag handling for this behavior was missing.
<ins>Solution</ins>
This PR handles the addition of the ON_PAGE_UNLOAD run behavior to the
ActionRunBehaviour enum, updates UI and settings to support it,
leverages feature flags for dynamic option availability, and adds tests
to ensure robust behavior.
Fixes#40995
_or_
Fixes `Issue URL`
> [!WARNING]
> _If no issue exists, please create an issue first, and check with the
maintainers if the issue is valid._
## Automation
/ok-to-test tags="@tag.JS"
### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results -->
> [!TIP]
> 🟢🟢🟢 All cypress tests have passed! 🎉🎉🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/15774903938>
> Commit: fe0b50052e7e8a0d1f74f75016657ca78ea25c7d
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=15774903938&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.JS`
> Spec:
> <hr>Fri, 20 Jun 2025 09:27:32 UTC
<!-- end of auto-generated comment: Cypress test results -->
## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [ ] No
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
- **New Features**
- Introduced a new "On page unload" run behavior option for actions and
JS functions, allowing actions to be triggered when a page is unloaded.
- Added a feature flag to enable or disable the "On page unload" run
behavior.
- **Enhancements**
- Run behavior options in the editor now dynamically update based on
feature flag settings, ensuring only valid options are shown.
- **Tests**
- Added comprehensive unit tests for utility functions handling run
behavior options and defaults.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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