Generate an integration test in `linera project new`

[jvff]

Motivation

When using linera project new to create a new application project, there's no obvious path to add an integration test. The developer must know how to use linera_sdk::test and that they need to enable the wasmer (or wasmtime) feature from linera-sdk in order to access the integration test facilities.

Proposal

Include a simple integration test template that maybe executes an operation and a query.

The template is located in linera-service/template.

The Crowd-Funding example application has an example integration test.