Add `cargo collect-metadata` as an cargo alias for the metadata collection lint
This PR adds a new alias to run the metadata collection monster on `clippy_lints`. I'm currently using it to create the `metadata_collection.json` file and I plan to use it in the `deply.sh` script. Having it as a new alias enables us to simply use:
```sh
cargo collect-metadata
```
It sometimes requires running `cargo clean` before collecting the metadata due to caching. I'm still debating if I should include a cargo clean as part of the `run_metadata_collection_lint` test or not. Input on this would be greatly appreciated 🙃
That's it, just a small change that can be reviewed and merged in parallel to #7214.
---
See: #7172 for the full metadata collection to-do list or to suggest a new feature in connection to it.
---
changelog: none
r? `@flip1995` btw. feel free to pass these PRs one to other team members as well if you want.
6bbee5c584