Add an apollo rover template

[paulpdaniels]

Rover allows us to specify a template that that users can invoke to bootstrap their subgraph: https://github.com/apollographql/templates

We should make one for caliban.

[ghostdogpr]

The template's repository should be located under the same account or organization as the primary library. For example, a template for Apollo Server should be located under the apollographql organization.

Can we have it inside this repo or does it need to be a separate repo?

[paulpdaniels]

@ghostdogpr We'd probably need to have a separate repo. I think it needs to be a top level repo that can be spun up into a new clone.