Umbraco Forms `Adding an Export Types` docs should include localization docs

[mattbrailsford]

What type of issue is it?

Missing documentation

What article/section is this about?

https://docs.umbraco.com/umbraco-forms/developer/extending/adding-a-exporttype

Describe the issue

Umbraco Forms Export Types use localization to populate their Label + Description in the UI. These docs need updating to detail that process. For this to work it is also required that the Export Type has an Alias property so the existing code examples will also need updating accordingly.