Create an Enum that specifies the available triggers

[thedrow]

Currently, we use strings as the trigger names.
We can use an Enum which specifies the list of available triggers for the state machine and use it in our codebase.

Example:

class ActorStateMachineTriggers(str, Enum):
    def _generate_next_value_(name, *args):
        return name.lower()

    initialize = auto()
    start = auto()
    stop = auto()
    restart = auto()
    report_error = auto()