Allow to set `lockfile-path` via an environment variable

### Problem

In https://github.com/rust-lang/cargo/pull/14326, the capability to specify an `lockfile-path` was added to cargo. It would be awesome if this would also possible to configure via an environment variable, similar to `CARGO_TARGET_DIR`.

### Proposed Solution

Add the capability to set the lockfile path via a `CARGO_LOCKFILE_PATH` environment variable.

### Notes

See also #14421