This pr make possible to add a new parachain to a running network (see
`add_para.rs` example), for that we allow to create a new parachain
config (using the same builder but in a different context) like this:

```rs
let para_config = network.para_config_builder()
        .with_id(100)
        .with_default_command("polkadot-parachain")
        .with_collator(|c| {
            c.with_name("col-100-1")
        })
        .build()?;
```
And then deploy that parachain by calling `add_parachain` (the second
parameter of the fn allow to use a custom chain-spec for the
relaychain).

```rs
network.add_parachain(&para_config, None).await?;
```

// TODO:
- [x] docs
- [ ] test (integration)

* wip, refactor provider trait

* fmt

* wip

* wip, add from_config to NetworkSpec

* config reorgs

* add logic for create NetworkSpec

* feat: refactored FileSystem trait and errors

* chore: removed unused local_file, stdout will be hardcoded in provider at the moment

* feat: moved MockFileSystem to InMemoryFileSystem, files too, and added mirror implementation of tokio::fs with tests

* feat: added new method append to FileSystem trait

* feat: implemented new append method on InMemoryFileSystem

* feat: added anyhow dependencies to support crate

* feat: refactored FileSystem trait to expose only a single wrapped error

* feat: refacto InMemoryFileSystem following FileSystem trait refacto

* feat: added conversion between io::Error and FileSystemError

* feat: added implementation of LocalFileSystem using tokio::fs

* feat: added nix crate dependency to workspace and provider crate

* feat: added uuid with v4 as dev-depen...