Refactor on startup configuration, sqlalchemy session maker, and email sender factory.

[Akin01]

There are 3 refactors that happens to this PR:

• change session maker to use async_sessionmaker instead of sessionmaker

# async_sessionmaker import from sqlalchemy.ext.asyncio
AsyncSessionFactory = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)

async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
    async with AsyncSessionFactory() as session:
        yield session

• Fastapi doesn't provide on_event now to setup lifespan event. But It can be setup directly to fastapi instance as lifespan attributes. Just create context manager generator to setup lifespan event. Ref: https://fastapi.tiangolo.com/advanced/events/

@asynccontextmanager
async def lifespan(_fastapi: FastAPI):
    if broker.is_worker_process:
        # TaskIQ configurartion so we can share FastAPI dependencies in tasks
        await broker.startup()
    
    yield

    if broker.is_worker_process:
        # On shutdown, we need to shutdown the broker
        await broker.shutdown()

• The last is provide custom factory to enable setter for sender globally

# Custom factory to be able to set the sender globally
class EmailSenderFactory(EmailSender):
    @property
    def sender(self):
        return self.sender
    
    @sender.setter
    def sender(self, sender: str):
        self.sender = sender

[devraj]

Hey @Akin01 thank you so much for this and pointing out those changes in SQLAlchemy and FastAPI. I will review this and merge it in.

Seeing you forked the repository, I am interested to know if you are using any portion of the template. Would love to learn more.