Description:

Stubs out a new experiment and its variants. Pass the experiment name,
either CamelCased or under_scored, and a list of variants as arguments.

To create an experiment within a module, specify the experiment name as a
path like 'parent_module/experiment_name'.

This generates an experiment class in app/experiments and invokes feature
flag, and test framework generators.

Example:

`rails generate gitlab:experiment NullHypothesis control candidate alt_variant`

NullHypothesis experiment with default variants.
    Experiment:   app/experiments/null_hypothesis_experiment.rb
    Feature Flag: config/feature_flags/experiment/null_hypothesis.yaml
    Test:         test/experiments/null_hypothesis_experiment_test.rb