Merge sync and async operator sensor

[Pankaj Singh]

Merge sync and async operator sensor

depend on #33

• Merge FivetranOperator and FivetranOperatorAsync, keep operator name FivetranOperator and add param deferrable=True|False
• Merge FivetranSensor and FivetranSensorAsync, keep sensor name FivetranSensor and add param deferrable=True|False
• Use pytest accross unit tests
• Deprecate existing FivetranSensorAsync and FivetranOperatorAsync

[Peter Huss]

Please see #45