`requests.certs.where()` is inacurate

Using a custom CA bundle as described in the docs I created an environment variable `REQUESTS_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt` and requests correctly uses this variable.  However, `python3 -c "import requests; print(requests.certs.where())"` still returns the ca bundled with certifi.  This is misleading

## Expected Result

I expected `python3 -c "import requests; print(requests.certs.where())"` to return `/etc/ssl/certs/ca-certificates.crt`.

## Actual Result

`python3 -c "import requests; print(requests.certs.where())"`  returned `/usr/local/lib/python3.6/site-packages/certifi/cacert.pem`

## Reproduction Steps

```bash
export REQUESTS_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt
```

```python
import requests
print(requests.certs.where())
```

## System Information

    $ python -m requests.help

```json
{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "2.0.7"
  },
  "cryptography": {
    "version": "35.0.0"
  },
  "idna": {
    "version": "3.3"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.6.13"
  },
  "platform": {
    "release": "5.11.0-1019-aws",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "101010cf",
    "version": "21.0.0"
  },
  "requests": {
    "version": "2.26.0"
  },
  "system_ssl": {
    "version": "1010104f"
  },
  "urllib3": {
    "version": "1.26.7"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": true
}
```

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Hi @nniehoff, 

Could you clarify what you find misleading? The docstring at the top of the certs module reads:

> This module returns the preferred default CA certificate bundle. There is only one — the one from the certifi package.

The functionality is pretty clearly documented and `requests.certs.where` is just an alias for certifi's `where`. That method is only intended to find the certifi cacert.pem file and doesn't provide any functionality for looking up other certs.

Sure, I completely expect the certifi package to return the cacerts bundle that is bundled with it.  However, IMO `requests.certs.where` isn't querying the certifi package but it is querying the requests package.  I would expect `requests.certs.where` to return the actual path the requests module is using.  In my case the value of the `REQUESTS_CA_BUNDLE` but looking at [this](https://github.com/psf/requests/blob/b0e025ade7ed30ed53ab61f542779af7e024932e/requests/sessions.py#L718-L719) I believe it could also be the value of the `CURL_CA_BUNDLE`  environment variable.  

I guess my suggestion would be `requests.certs.where` should override `certifi.where` and return either of the variables if set or default to the value of `certifi.where`

Ok, thanks for clarifying. So it seems our documentation and the functionality is consistent, this is just a feature request for additional behavior. The proposal is a deviation from the current documented behavior that will likely negatively affect anyone using this specifically for `certifi`'s location.

Given that the feature is easily done with ~5 lines of Python locally, I'd advise writing a quick helper function for that for the time being. We may reconsider this if we release a new major version, but I'm going to close this for now since I don't think we'll see a change to this in the near future.