Update sentry error handling documentation (#2990)
Update sentry error handling documentation (#2990)

- Change examples to use the Sentry Python SDK: `sentry-sdk`
- Removed the app factory pattern example
- Added a custom exception handling example
pallets/flask,fkazimierczak/flask,pallets/flask,fkazimierczak/flask,mitsuhiko/flask,mitsuhiko/flask,drewja/flask,pallets/flask,fkazimierczak/flask,drewja/flask,drewja/flask