[Index Template] Preview strips dataStream prop making it impossible to preview a data stream

[Dosant]

Kibana version: main

Describe the bug:

When you create a template for data stream

And then you click "Preview index template" in one of the steps, and the template is previewed as if the data stream option is off.

The dataStream prop on a template is removed here because it is an empty object, and it is striped:

kibana/x-pack/plugins/index_management/public/application/components/index_templates/simulate_template/simulate_template.tsx

Line 38 in bc2a181

const indexTemplate = serializeTemplate(stripEmptyFields(template) as TemplateDeserialized);

We don't hit this problem when we save the template because the strip function is used only to remove empty strings:

kibana/x-pack/plugins/index_management/public/application/components/template_form/template_form.tsx

Lines 228 to 230 in bc2a181

	stripEmptyFields(template, {
	types: ['string'],
	}) as TemplateDeserialized

Any additional context:

This is important for #130715 because when we create a template for a time series data stream, we don't need to specify index routing, but it is required for index. This bug makes preview functionality not used when creating a template for time series data stream

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesUx)

[elasticmachine]

Pinging @elastic/platform-deployment-management (Team:Deployment Management)