Dependency improvements

[tomwhite]

Lithops has a lot of dependencies in the base package, many of which are not needed when running Lithops.

There are a few things we could do here:

1. Move dependencies for backends into 'extra' packages
   • boto3 - move to lithops[aws] (see Move boto3 package into lithops[aws] extra #1323)
   • ibm* - move to lithops[ibm]
   • kubernetes?
2. Make dependencies for optional features optional
   • redis
   • pandas/matplotlib/seaborn - for plotting
3. Remove unused dependencies
   • lxml

[JosepSampe]

If I'm not wrong, the docker and the python-dateutil packages can also be removed. I remember they were used in the past, but now I can't find any import of these libraries.

[JosepSampe]

@gilv Do you agree on moving IBM dependencies from the default installation to extra packages? so that when using an IBM backend, users will have to install lithops like this: pip install lithops[ibm]?