Templates: removing notion of Stargate

[lumtis]

In many places in the template package, we use the notion of stargate. Like the default name for the template folder of list for example

Is it still pertinent to use this naming now that stargate has been the only supported version for a while and it might be confusing for new users getting to the codebase and that don't have the context on launchpad/stargate?

Suggested change:

templates/
  typed/
    list/
      stargate/
        component/
        messages/
      stargate.go

-->

templates/
  typed/
    list/
      component/
      messages/
      list.go