Add docs for execution order of listeners

[Ronserruya]

I noticed an undocumented behavior with listeners, where some of them run in reverse order of registration

1. What is the rationale for that?
2. Can this be added to the docs?

Additional context
Relevant lines of code from https://github.com/huge-success/sanic/blob/master/sanic/app.py#L1356

 # -------------------------------------------- #
        # Register start/stop events
        # -------------------------------------------- #

        for event_name, settings_name, reverse in (
            ("before_server_start", "before_start", False),
            ("after_server_start", "after_start", False),
            ("before_server_stop", "before_stop", True),
            ("after_server_stop", "after_stop", True),
        ):
            listeners = self.listeners[event_name].copy()
            if reverse:
                listeners.reverse()
            # Prepend sanic to the arguments when listeners are triggered
            listeners = [partial(listener, self) for listener in listeners]
            server_settings[settings_name] = listeners

[stale]

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[Tronic]

This convention comes from Python with statements, C++ RAII and similar constructions of scope bound resource management. The rule is that you should deconstruct in exact reverse order of construction.

For instance, if your first before_server_start handler setups a database connection, ones registered after it can rely on that connection being alive both when they are started and stopped, because stopping is done in reverse order, and the database connection is torn down last.

Perhaps it should be documented. Pull requests are welcome. Look at docs/sanic/

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If this is incorrect, please respond with an update. Thank you for your contributions.

[tomaszdrozdz]

@ahopkins @Tronic Can we close this issue ?