Support dynamic template properties

I have a custom workspace template that (during initialisation via the TRE UI) requires a TRE admin to specify a string property value, that is an ID of a previously created TRE workspace . However, ideally I'd like to display a list of existing TRE workspace IDs in a dropdown, to avoid the user entering an ID of workspace that doesn't exist.

While it's possible to specify custom workspace template properties by including properties with an enum attribute to generate such a list of options. As far as I can tell its only possible to define an enum for a property statically in the template_schema.json file of the workspace template.

From looking at the code, one way to do this dynamically might be to define a property in template_schema.json that indicates that the property is dynamic and that the TRE UI app when rendering the workspace template form should make an additional API calls to populate the enum of the property with the relevant data e.g.

 "primary_workspace_id": {
      "type": "string",
      "title": "Primary Workspace Identifier",
      "description": "List of existing workspace IDs",
      "dynamic_enum": {
           "api_call":"api/workspaces",
           "property_name":"workspace_id"
      }
    }

I'm not a React developer but the rendering appears to happen here >> https://github.com/microsoft/AzureTRE/blob/de141651ad9fb9f58e7b78e383edf263eaa549d1/ui/app/src/components/shared/create-update-resource/ResourceForm.tsx#L31C2-L50C1

So once the chooen workspace template is returned from cosmosdb, the list of properties are processed and where a dynamic property is found an additional handler performs the nessasary API call to populate the enum before the form data is set. For my specific case I'm able to reuse the existing TRE API calls (i.e. api/workspaces) without modification.

Any thoughts on this or best approaches to supporting this feature in the TRE?

Start with ui/app/src/components/shared/create-update-resource/ResourceForm.tsx and the workspace template_schema.json property handling, focusing on how static enum values are rendered. Trace the existing api/workspaces call and determine how a dynamic property could populate its options before the form is initialized. Done means a template can declare a dynamic property and the TRE UI displays current workspace IDs for selection.