Antares depending on a non-pip kafka package

[olivialynn]

This is a reminder to follow up on the kafka hotfix I made in #132.

If this is in fact the best solution, we should at least add a line about installing librdkafka in our own installation instructions.

Unfortunately, librdkafka does not seem to be available via pypi, which impacts superphot-plus on pypi.

[hombit]

The most frustrating part that we don't actually use kafka within antares-client. In #132 I propose separating training-specific packages to a new extras, so antares-client would not be a requirement for users who do not need fetching the data.

[olivialynn]

I went ahead and merged 132 to give us access to unit tests again, but I do really like the idea of separating these packages out - if I have time today I'll start looking into it!

[olivialynn]

Considering moving alerce even out of the "dev" package section.

Reasoning being: on ubuntu you just need to run apt-get install librdkafka-dev before pip installing antares - but on Mac M1, you need to:

• brew install librdkafka
• and then add (updating to your specific version of librdkafka):

export C_INCLUDE_PATH=/opt/homebrew/Cellar/librdkafka/2.2.0/include
export LIBRARY_PATH=/opt/homebrew/Cellar/librdkafka/2.2.0/lib

to your zshrc file, as python apparently doesn't look into brew directories unless directed (described in https://stackoverflow.com/a/72771461). (Noting you could opt to set the vars via command line if desired)

A solution for now could be simply describing this process in the documentation (wordy, annoying for M1 users, may be overlooked by someone just trying to quickly install; however, our target end users are probably mostly using Ubuntu machines anyway, I believe?)

If we "quarantined" the antares_client dependency out of .[dev], dev installation could look something like:

Most cases:
pip install -e .
pip install '.[dev]'

Include antares on ubuntu:
pip install -e .
pip install '.[dev]'
apt-get install librdkafka-dev
pip install '.[data-generation]'

Include antares on Mac M1:
pip install -e .
pip install '.[dev]'
brew install librdkafka
vim ~/.zshrc
add in the two lines of environment variables
pip install '.[data-generation]'