xtask: sovereign binaries execution

[gabriele-0201]

Duct does a weird thing with dir. You can find more information about it here: docs.rs/duct/latest/duct/struct.Expression.html#method.dir and the following code snippet does not work:

let sovereign_rollup_handle = cmd!("../target/release/sov-demo-rollup")
   .dir("demo/sovereign/demo-rollup/")
   .run()?;

To solve this issue, you can change the references to the folder demo/sovereign/test-data. Currently, the sov-demo-rollup and sov-cli binaries expect to be executed from the folder demo/sovereign/demo-rollup, and every reference to test-data is ../test-data. We could modify it to be executed from the main directory of the project, so that all relative paths to test-data will be demo/sovereign/test-data, and there won't be conflicts with how relative paths are handled by duct::dir.

Here's how it could look like if we make such change:

let sovereign_rollup_handle = cmd!("demo/sovereign/target/release/sov-demo-rollup").run()?;

the test function would then be

let cli = "demo/sovereign/target/release/sov-cli";
let test_data_path = "demo/sovereign/test-data/";
let run_cli_cmd = |args: &str| duct::cmd(cli, args.split(' ')).run();

As you can see, there would no longer be a need to execute sh commands with duct