Env-driven OTLP trace export built its resource from only service.name,
so OTEL_RESOURCE_ATTRIBUTES entries were silently dropped and backends
that attribute spans via resource attributes never received them.
Merge the vendored envDetector into the resource, which parses
OTEL_RESOURCE_ATTRIBUTES (percent-decoded, per spec) with OTEL_SERVICE_NAME
taking precedence for service.name.
Fixes#7134
