CLI stub for Fourier discrimination

This adds a stub of CLI mimicking what we describe in ADRs. Since there are no unit tests for the stubs, here is how to test it:

switch to the branch from this PR
important reinstall PyQBench, because entrypoitns are not updated even if it is installed in editable mode:
```
pip install -e .
```
verify that qbench script is available in your path now by running:
```
qbench -h
```
verify that the CLI matches the one described in ADRs

iitis / PyQBench