[client-reports] Include event processors and before send

[smeubank]

On Python and JS sdks there is now the added functionality to gather information from client side and send to sentry. The JS SDK is currently gathering more outcome types for discarded events than Python. They should gather as much as possibly the same metrics

• event_processors & before_send

https://develop.sentry.dev/sdk/client-reports/

original client report support PRs for both SDKs

getsentry/sentry-javascript#3955
#1181