fix(bunny): headers property needs to exist

[maciekm]

bunny instrumentation errors when rabbitmq messages don't have headers property, e.g. published by an app that isn't instrumented yet.

E, [2023-09-07T12:01:06.688026 #1] ERROR -- #<Bunny::Session:0x29d88 hidden@hidden:5672, vhost=hidden, addresses=[hidden:5672]>: Uncaught exception from consumer #<Bunny::Consumer:101200 @channel_id=1 @queue=hidden @consumer_tag=hidden>: #<NoMethodError: undefined method `[]' for nil:NilClass 

carrier[key]
^^^^^> @ /gems/ruby/3.1.0/gems/opentelemetry-api-1.2.2/lib/opentelemetry/context/propagation/text_map_getter.rb:16:in `get'

you can reproduce the issue by spiting the example file into a publisher without instrumentation and a consumer with.

[linux-foundation-easycla]

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• ✅ login: maciekm / name: Maciej Moleda (1331aa0, b3685c2)

[arielvalentin]

@maciekm I have not had much success in tracking down or getting feedback from the original contributors.

Would you be willing to take over as the maintainer of this instrumentation?

Also would you be able to look into why this instrumentation has multiple sets of Trace Context Propagation Carries in the properties i.e. headers and tracer_receive_headers?