Refactor RB to inherit from experiment class

[ShellyGarion]

What is the expected behavior?

Add the following experiments:

• Standard RB Experiment
• RB utils
• Interleaved RB
• CNOT-Dihedral RB
• Interleaved CNOT-Dihedral RB
• Purity RB

Depends on merging the Experiment base classes from #514

[ShellyGarion]

Future plans:

• Simultaneous RB experiments, running various RB patterns (by using joint experiment classes)
• Correlated RB (correlated RB fitter #434)
• Leakage RB ([WIP] Leakage RB fitter #480, [WIP] create leakage rb example #496)
• Add measurement error mitigation for certain RB experiments (purity, leakage and correlated)

[ShellyGarion]

Moving to qiskit-experiments