Detect and use Alire metadata found in pinned directory (#450)

Detect and use Alire metadata found in pinned directory (#450)

* Detect crate at linked dir and use its deps/paths

If a path given to with/pin --use contains a loadable alire workspace (i.e.,
for a crate manually initialized, or retrieved with `get`), the release found
there will be used to retrieve additional dependencies, and its project paths
will also be used.

* `with` directory with autodetection of crate

When adding a dependency as a pinned dir, and the target dir is a regular Alire
crate, we can autodetect the crate we are adding as dependency. In that case
the command becomes `alr with --use <path>`. This can also be useful in the
future for remote URLs that will also provide the crate being retrieved.

* Refactor --url to --use