fix: add a constructor that accepts AaiMessage to ChangeHeadersRefCommand_Aai20 to fix change of message headers ref in apicurio

[ben-lc]

Hi,
I'm new to apicurio so I will appreciate any advice regarding this PR if I did something wrong.

This PR is related to Apicurio/apicurio-studio#2737

I tried to use ChangePropertyCommand as suggested by deprecated doc in ChangeHeadersRefCommand_Aai20,
but since we have to create headers node on the message node if headers is null, it's not possible to use ChangePropertyCommand cause it only works with simple types.
I ended up updating ChangeHeadersRefCommand_Aai20 and bringing same modifications that were done to ChangePayloadRefCommand_Aai20 to support a constructor with AaiMessage.

[EricWittmann]

Hi @ben-lc I think this looks good, but it's a nice opportunity to add a test for the use-case you're trying to fix. It should be very easy to do. Have a look at the test framework for commands here:

https://github.com/Apicurio/apicurio-data-models/blob/1.x/src/test/resources/fixtures/cmd/tests.json

You just need to follow the pattern in that file (and obviously the files it points to). :)

wdyt?

[ben-lc]

Hi @EricWittmann, thanks for your feedback, I've added the test for this use case.

[EricWittmann]

👍👍

[EricWittmann]

Merged!