Dropdown - emit msg on event

[bartbutenaers]

Description

This PR adds a new option to the ui-dropdown node to select when an output message should be triggered:

As explained in the info panel:

This msgTrigger property can also be dynamically set. The default value is "onChange" like in the previous versions, to avoid breaking changes.

The following example flow demonstrates the default "onChange" value, which is then dynamically overwritten by a "onClose" value:

Related Issue(s)

Closes 1457

Checklist

• [X] I have read the contribution guidelines
• [ ] Suitable unit/system level tests have been added and they pass
• [X] 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

[bartbutenaers]

P.S. I used the @blur event, because @close was never triggered. See this discussion.

[joepavitt]

Thanks @bartbutenaers - great stuff.

Apart from a shift of where the form-row is in the config, and the labels used, this is good to go as far as I'm concerned. I'll be merging once the tests give me the green light.