Document precedence order is multiple context propagators are used

[pavolloffay]

    ContextPropagators contextPropagators = DefaultContextPropagators.builder()
        .addHttpTextFormat(new JaegerPropagator())
        .addHttpTextFormat(new HttpTraceContext())
        .build();
    OpenTelemetry.setPropagators(contextPropagators);

The DefaultContextPropagators.Builder should document precedence order when multiple context propagation formats are used - especially for extraction. At the moment all formats are extracted and the last one is returned.

opentelemetry-java/context_prop/src/main/java/io/opentelemetry/context/propagation/DefaultContextPropagators.java

Line 72 in 690651b

public static final class Builder {