Documentation for streams in spec is needed

[bird-dancer]

Currently it is unclear for a user how streams are to be declared.
It is also not done in a uniform manner eg. in

AsyncAPI/example/specs/basic_queues_and_stream.yaml

Line 14 in d05d047

x-streamname: testStream

it is x-streamname and in

AsyncAPI/example/specs/test_stream.yml

Line 14 in d05d047

streamname: testStream

it is streamname

How to use this in the specs and templates needs to be documented.
Is marked as a bug since this feature is unusable for a third person because of this.