Templating: Creating a doctype with template now yields a strongly typed template (closes #20443)

[lauraneto]

Fixes #20443

In recent versions the flow of requests from the client when creating a document type with a template was:

1. Create a template.
2. Create a document type with the template id returned in 1.

In 1., the document type still didn't exist, so a "generic" template was being created.
Additionally, if the creation of the document type failed, the "orphan" template would remain.
This PR adds a new endpoint to the Management API:

POST /umbraco/management/api/v1/document-type/{guid}/template
{
  "alias": "templateAlias",
  "name": "templateName",
  "isDefault": false // Whether to set this template as the default for the document type
}

With the above in place, I adjusted the flow to:

1. Create document type (with no template)
2. Create template using the new endpoint (which will assign the template as default as well)

This way, a template is only created if the content type was actually created, and the generated template will know which model to reference.

The idea while building the new endpoint was also that you can also create templates for document types later on, default or not.

Testing
Create a Document Type with Template and verify that the generated template references the typed model and looks the same as in V13.
Also, ensure that creating templates through the backoffice still works as expected.

[Copilot]

Pull request overview

This PR refactors the document type creation flow to prevent orphaned templates. Previously, templates were created before document types, which could leave orphaned templates if the document type creation failed. The new approach creates the document type first, then creates the template via a new Management API endpoint (POST /umbraco/management/api/v1/document-type/{id}/template). This ensures templates are only created for successfully persisted document types and allows the server to generate templates with the correct model reference.

Key changes:

• Introduces a new API endpoint for creating templates linked to specific document types
• Moves template creation logic to occur after document type creation
• Adds CreateTemplateAsync method to IContentTypeService and ITemplateService

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
document-type-workspace.context.ts	Refactored _create to call template creation after document type creation; replaced direct template repository usage with document type template repository
document-type-template.repository.ts	New repository for managing document type-specific template operations
document-type-template.server.data-source.ts	New data source that calls the new Management API endpoint
types.ts	Added UmbDocumentTypeTemplateModel type definition
TemplateService.cs	Added new overload for CreateForContentTypeAsync accepting name, alias, and content type alias parameters
ContentTypeService.cs	Added CreateTemplateAsync method that creates a template and assigns it to a content type
CreateDocumentTypeTemplateController.cs	New API controller implementing the template creation endpoint
CreateDocumentTypeTemplateRequestModel.cs	Request model for the new endpoint
content-type-workspace-context-base.ts	Added reload() method to refresh workspace data
content-type-structure-manager.class.ts	Added reload() method to fetch latest content type data

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[Copilot]

The return type is cast to string, but the API endpoint returns the template's GUID. The comment in the controller shows it returns the template key, not a string. This should likely be return { data: data as Guid } or the appropriate type representing a GUID.

[AndyButland]

Looks good to me @lauraneto, and tests out as expected. Just a couple of inline comments to consider, and a response to your question.

Just wonder if you might look at ContentTypeServiceTests and see if it's worth adding a test or two to cover the CreateTemplateAsync method you have added, and similar for CreateForContentTypeAsync added to TemplateService.

[AndyButland]

Maybe we should introduce InvalidTemplateAlias as a new result option here? Just seeing as we have InvalidAlias and InvalidPropertyTypeAlias already.