Enhancement: `kpm add` should support adding local kcl packages as references.

## Enhancement
Not all dependencies come from the network, and kpm should be able to manage local dependencies.

By `kcl.mod`.

```
[dependencies]
my_pkg = { path = "/usr/my_pkg" }
```

Or by command:

```
kpm add /usr/my_pkg
```

`/usr/my_pkg` is the directory contains `kcl.mod`.