`pip.parse` should allow hiding transitive dependencies

# 🚀 feature request

### Relevant Rules

`pip.parse`

### Description

Given a `requirements.in` file containing only `foo==4.2.0` from which I create a lock file with content
```
foo==4.2.0 --hash=
dep_of_foo==1.33.7 --hash=
```

When using `pip.parse` to crate a hub `@pypi` from this lock file users can access all Python modules from the lock file. Concretely, `@pypi//foo` and `@pypi//dep_of_foo`.

I consider `dep_of_foo` an implementation detail which no user should depend on. When changing the version of `foo`, then `dep_of_foo` might vanish or change drastically as side effect. If I wanted users to access `dep_of_foo`, I would have added it to the `requirements.in` file to make it an explicit and desired direct dependency of my project.

It would be great if there were an option enforcing that transitive dependencies are not available to users.

### Describe the solution you'd like

Ideally `pip.parse` would offer an attribute `restrict_visibility_to` (or any other name) which takes a file list. Then, one could provide one or multiple `requirements.in` files to this attribute. `pip.parse` can then read those files, extract the Python module names and ensure only those are public targets in the pip hub.

The implementation would be easier if `restrict_visibility_to` takes a list of strings and the user explicitly states which Python modules should be public. However, I consider this inferior, as it increases the maintenance burden whenever changing the `requirements.in` files.

### Describe alternatives you've considered

I implemented the described behavior locally as a workspace rule, which creates a new hub with alias targets pointing to the hub created by `pip.parse`. It is trivial to do so, not much logic is required.

However, this means one has to teach people not to use the original hub created by `pip.parse`. Or one has to write yet another piece of custom code for a BUILD file checker ensuring this rule.
Overall, it would be much nicer if this behavior would be a feature of upstream `pip.parse`.

`pip.parse` ルールから始め、`requirements.in` の入力を生成されたロックファイルおよび pip ハブターゲットと比較します。意図された可視性の境界を理解するため、issue で説明されているローカル workspace ルールと BUILD-file チェッカーの代替案を確認します。直接依存関係が公開されたままになり、重複したカスタムルールを必要とせずに推移的依存関係が非表示になれば完了です。

索引モデルが issue の本文から書いたものです。