Switch deprecated startup events to lifespan events

[alyssadai]

The @app.on_event("startup") syntax seems to be deprecated: https://fastapi.tiangolo.com/advanced/events/#alternative-events-deprecated and replaced by https://fastapi.tiangolo.com/advanced/events/#lifespan

We should look into updating the startup checks for defined credentials and allowed origins to follow this new syntax.

Originally posted by @surchs in #151 (comment)

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We want to keep our issues up to date and active. This issue hasn't seen any activity in the last 75 days.
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[samadpls]

Hi @alyssadai, Can i take this issue? 😋

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We want to keep our issues up to date and active. This issue hasn't seen any activity in the last 75 days.
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When you review, please reread the spec and then apply one of these three options:

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