Rename `nlp` variables into more appropriate names
# 🚀 Feature request

In `pipelines` tests and documentation they are recurringly named `nlp`, the goal is to rename them to something more appropriate.

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## Motivation


```python
nlp = pipeline(task='conversational', model='XXX')
```
This is a bit pretentious as it does cover all NLP, and a better name help understanding to users too.
For instance the `conversational` task pipeline could be named `conversational_agent`. Or maybe still a generic name but less
pretentious `pipe`, `pipeline` (caveat: those are less clear in what they intend to achieve)

The goal is to rename all occurences of `nlp` by better names within both tests and the documentation.


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## Your contribution

The better names could be discussed here.

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Thanks for creating the issue! Here are examples of what good names are in my humble opinion:
```
classifier = pipeline("sentiment-analysis")
unmasker = pipeline("fill-mask")
text_generator = pipeline("text-generation")
```
In short, something that describes the task it achieves.<|||||>Hi guys, I'm new and I'd like to start helping out. Can I take over this request? And to clarify, you're referring to the references primarily in the /tests directory and in the /docs directory?<|||||>Hi @terrenceedmonds , Thanks for taking this on ! 

Yes, for both directories, but docs are also found within docstrings within the `src/transformers/pipelines` directory.<|||||>Hii. Is this issue still open? I want to take this issue. Also, this will be my first contribution. Any help in getting me started will be highly appreciated.<|||||>Let's see if @terrenceedmonds wants to to finish it first (the PR was almost ready to merge).<|||||>Can I work on this issue, if @terrenceedmonds is not working on it?<|||||>Yes, you can go ahead!