Add on_start and on_shutdown lifespan hooks

[cirospaciari]

on start and on shutdown hooks with async and sync support is very useful when using CLI tools to do start and cleanup things.

from socketify import App

app = App()

@app.on_start
def on_start():
    pass

@app.on_shutdown
def on_shutdown():
    pass

• Add start hook
• Add shutdown hook
• Add CLI support
• Add Documentation