Faster dogfooding of Python SDK in `sentry`.

Sometimes it takes weeks until we update `sentry` after a new version of the SDK is released. `sentry` should always use the most recent version of the SDK for best dog fooding.

Set up dependabot in `sentry` to also check the Python SDK, and make sure that the Web Backend SDK gets a notifiction when dependabot creates a PR, so we can semi automate this step.

Start by inspecting the `sentry` repository's existing Dependabot configuration and how the Python SDK is currently updated. Define the notification path for the Web Backend SDK when Dependabot opens a PR, then verify that the latest SDK receives update checks and that the notification is sent; no specific file or test is named in the issue.

Scritto dal modello di indicizzazione a partire dal testo della issue.