Tracing without Performance

[stephanie-anderson]

See getsentry/team-sdks#5

Tasks

Beta Give feedback

1. All events are always sent through the /envelope endpoint if performance is enabled. (If possible just always use /envelope) feat: Remove store endpoint #631
2. Add a mechanism to continue a trace from environment variables.
3. All error, transaction and check-in events sent to Sentry always contain a Dynamic Sampling Context (trace) envelope header item.
4. All error, transaction and check-in sent to Sentry always contain a trace context.