Implement PulserPasqal module

[CdeTerra]

Developers do not need to directly access the CloudSdk anymore, thanks to the new PasqalCloud class and aliases (see the UT file for an example).

@anneclairelh : I did some copy/paste of the docstrings of the CloudSdk. Is it okay for you that I use them? It helps developers to check them easily from the documentation.

[HGSilveri]

Ok, I can see we have an issue with the supported Python versions since cloud-sdk starts from Python 3.8... Perhaps it's a good time to consider dropping support for Python 3.7 in pulser altogether.

[CdeTerra]

Thanks all for your comments! I will fix flake8's errors that appear on the CI (strangely, it passes locally).

EDIT: It's because I forgot to git add some files.