Add optional message description for manual consumer/producer definition

[timonback]

Allow to set a optional description on the async api message object spec: https://www.asyncapi.com/docs/reference/specification/v2.0.0#messageObject

Demo code for kafka and amqp examples was added as well

Related change in springwolf-ui will follow

[timonback]

(FYI: I forked from HEAD-1, since the build on master is currently broken due to a change added in the last commit)

[stavshamir]

(FYI: I forked from HEAD-1, since the build on master is currently broken due to a change added in the last commit)

Yep, I will revert the last commit before merging this PR.

[timonback]

I updated the PR so that also the springwolf-example projects tests pass - in my fork.

The core build is broken as the gh action builds the merged branch, not the changes only.

[stavshamir]

Thanks for the nice addition @timonback :)