Add support for installing crates from path

[sagudev]

Currently, this is not possible, because action still tries to find crate in index.

[baptiste0928]

The action needs to generate a cache key that is invalidated whenever the crate changes, which in this will require computing some sort of hash of the crate's contents and its dependency tree. Since this will probably be a bit tricky to implement (and maintain in the future), I'm not sure it's worth adding.

Maybe try caching the /target directory instead? You can use something like Swatinem/rust-cache for this.