Exclude pip modules from reshim?

Hi there, I was wondering if it's possible to prevent some installed pip modules from being linked during a `asdf reshim python`.

For example, I have the `python-apt` module installed because I write python scripts to interact with apt, however this now overrides my base OS version's `apt` binary

I don't want to totally prevent python modules from being installed in my path because of things like `ansible`

```
~
$ apt --version
1.18

~
$ apt install apt
* Running: sudo apt-get install apt
Reading package lists... Done
Building dependency tree
Reading state information... Done
apt is already the newest version (2.0.9).
The following packages were automatically installed and are no longer required:
libfwupdplugin1 libxmlb1
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 20 not upgraded.

~
$ which apt
/home/ddastoor/.asdf/shims/apt

~
$ pip3 list | grep apt
apt-wrapper 1.18
pyapt 0.0.6
wrapt 1.15.0
```

Inizia riproducendo `asdf reshim python` con `python-apt` installato e analizza come viene generato lo shim `apt`. La modifica dovrebbe fornire un modo per escludere determinati comandi forniti da pip continuando a collegare comandi utili come `ansible`, lasciando disponibile `apt` di sistema.

Scritto dal modello di indicizzazione a partire dal testo della issue.