Function submit_payload 

pub fn submit_payload(
    payload: &TelemetryPayload,
    endpoint: &str,
) -> Result<SubmitOutcome>

Submit a telemetry payload to the given endpoint synchronously.

This function:

1. Validates the URL is HTTPS (rejects HTTP before network access)
2. Serializes and validates the payload
3. Sends the payload via HTTPS POST
4. Returns SubmitOutcome::Success on HTTP 200

Errors

Returns SubmitOutcome::HttpRejected for HTTP URLs. Returns SubmitOutcome::Failed for network or server errors.