Custom actions in properties panel header

[philippfromme]

Is your feature request related to a problem? Please describe.

While there are some customization options for the header (e.g. custom icon) the general content of the header is not customizable. Additional actions cannot be added.

The Web Modeler currently adds a Save as action by appending it to the DOM and positioning it absolutely.

Describe the solution you'd like

Be able to add custom actions to the properties panel header. These actions could be organized in a dropdown if there are many.

Describe alternatives you've considered

None. There's no other way to to customize the header.

Additional context

Web Modeler bug due to hacky implementation of the Save as action: https://github.com/camunda/web-modeler/issues/15151
Current refactoring efforts related to the Save as action: https://github.com/camunda/web-modeler/issues/14871#issuecomment-2962448141

[barmac]

Related to bpmn-io/bpmn-js-properties-panel#1123 though the scope is different.

[jarekdanielak]

Another use case is the integration of Task Testing (epic).