Sun-setting the `/store` endpoint

[antonpirker]

The /store endpoint to save events in Sentry is a legacy endpoint and should not be used anymore. Everything should be sent to the /envelope endpoint.

Here:
https://github.com/getsentry/sentry-python/blob/antonpirker/top-level-get-current-span-transaction/sentry_sdk/client.py#L443-L469