FX command - make it more independent

[rstoki]

Is your feature request related to a problem? Please describe.
During the initialization of the federation (federated environment), the fx command is very useful. However, it performs some "additional tasks", that are typically not required (or, in the future may be problematic), and need to be 'rolled-back' manually.

A list of non-necessary actions:

1. Do not call pip install -r requirements.txt``inside fx workspace create`

   • the command fx workspace create creates workspace from a template, but it also calls pip install -r requirements.txt inside.
     For example, for template tf_2dunet, it installs TensorFlow 2.3.1, which is non-current version as of 05/2021 -- the current version is 2.4.1. So typically, there is a big chance it will roll-back already installed (and working) tensorflow version in the user's python environment to the previous version, which may not be working for him. Moreover, if the user want to change/modify his model and/or supply his own pretrained one.

2. do not check data folders inside fx plan initialize

   • the command fx plan initialize take into consideration also data paths set in the <workspace>\plan\data.yaml file. But since the fx plan initialize is called on aggregator, and the data folders for individual clients are on a completely different computers, it must not be assumed they can be accessible from the aggregator.

Describe the solution you'd like

1. Do not call pip ... from fx tool
2. Do not check existence of data paths since the setup is performed on the Aggregator (which, by definition, do not have access to any data)

[rahulga1]

With recent changes, both of the ask have been taken care of.