Improve Colab setup experience by simplifying dependencies

[tholor]

When starting a tutorial in colab, the installation process is quite annoying (especially for first-time haystack users). Let's try to make it smoother and ideally avoid the need of "restarting the runtime" after the haystack installation.

1. Let's verify which of our dependencies does not match with the preinstalled Colab env. From a quick look it seem:

  Attempting uninstall: pillow
    Found existing installation: Pillow 7.1.2
    Uninstalling Pillow-7.1.2:
      Successfully uninstalled Pillow-7.1.2
  Attempting uninstall: grpcio
    Found existing installation: grpcio 1.42.0
    Uninstalling grpcio-1.42.0:
      Successfully uninstalled grpcio-1.42.0
  Attempting uninstall: pluggy
    Found existing installation: pluggy 0.7.1
    Uninstalling pluggy-0.7.1:
      Successfully uninstalled pluggy-0.7.1

It then only complains about PIL being already loaded and requiring a restart of the runtime:

WARNING: The following packages were previously imported in this runtime:
  [PIL]
You must restart the runtime in order to use newly installed versions.

2. Let's investigate if we can relax our version requirements here or which parts of Haystack would be affected in their functionality
3. Alternatively, if we can't avoid a restart let's check if there's an option to trigger the restart automatically

[nickchomey]

I've been getting this same error on Colab today while running Tutorial 6.

WARNING: The following packages were previously imported in this runtime:
  [PIL]
You must restart the runtime in order to use newly installed versions.

Is there something wrong with the code in that Tutorial or has this bug resurfaced, perhaps with the recent changes to the dependencies?