Fix extension compatibility issues with AWS Lambda Runtime Interface Emulator

[rebu-dt]

Fixes the following issues I encountered while trying to run an extension built with the lambda-extension crate in AWS Lambda RIE:

• AWS Lambda RIE returns status code 202 Accepted instead of 200 when emulating the Telemetry API (see the response codes on this page), which led to the error: unable to initialize the telemetry api: 202 Accepted. This patch accepts all status codes in the 200-299 range instead. I also changed similar occurrences for consistency.
• It looks like the tracing field on InvokeEvent is not set, so I made it optional. Please let me know if this change is too intrusive (maybe #[serde(default)] would be a better fit here?). Also see tracing field missing from Lambda extension INVOKE event aws/aws-lambda-runtime-interface-emulator#109

By submitting this pull request

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I confirm that I've made a best effort attempt to update all relevant documentation.
  • (probably not relevant here)

[calavera]

Can you format your changes?

[calavera]

We can merge it once we change Tracing to have a default instead of being an option.

[rebu-dt]

@calavera I've changed the tracing field to use #[serde(default)] and ran the formatter.

[calavera]

Thanks!