Title: X-Ray tracing plugin doesn't publish conformant segment document

Description:

Currently, the X-Ray tracing plugin publishes all fields as strings in the output JSON document. This is in violation of the datatypes defined by the X-Ray documentation, and results in X-Ray ignoring this fields when they are sent to the X-Ray service.

Repro steps:

Any Envoy configured with X-Ray tracing, for example

tracing:
  http:
  name: envoy.tracers.xray
  typed_config:
    "@type": type.googleapis.com/envoy.config.trace.v3.XRayConfig
    segment_name: ${SEGMENT_NAME}
    daemon_endpoint:
    protocol: UDP
    address: ${AWS_XRAY_DAEMON_ADDRESS}
    port_value: ${XRAY_DAEMON_PORT}