AMQP tracestate should be string

[lmolkova]

Consider changing tracestate to be encoded as string

Pros:

• AMQP libraries do not need to implement complex logic of parsing/serializing tracestate
• Same as prev: blind propagation must be extremely efficient and simple. User applications that use AMQP also likely use HTTP. If they never change tracestate - there is no need to serialize it back and forth.
• There are no bandwidth improvements coming from map usage
• On the implementation layer, using maps is not efficient: ordered dictionaries are not very efficient especially for a handful of items
• if tracestate parsing is controlled by tracing system, at least it can mitigate some of the perf impact parsing tracestate only on sampled in spans.

Cons:

• Tracing systems need to parse tracestate from string (needless to say, it already has to because of HTTP)

Overall tracestate is tracing system concern and it seems practical to save protocol implementations from dealing with tracestate specifics.

[lmolkova]

@SergeyKanzhelev @clemensv @calohmn @AloisReitbauer @yurishkuro @grs

[yurishkuro]

+1