Determine REST_CLIENT_REACTIVE_JACKSON capability properly

[chberger]

This PR fixes #499

Some thoughts on this PR:

• I'm wasn't able to write some automated tests. That's because the test setup would be quite complex. We would need to compile the extension with Quarkus 4.3.1 and would test the extension with a business app using Quarkus in a previous 3.X version. Anyhow, I was able to test the functionality manually. Up to you if this would be good enough to continue. Otherwise somebody else is most welcome to write such a test.
• This code can be reverted as soon as we drop support for Quarkus versions earlier than 3.4.1
• I did some further testing and it looks like quarkus-openapi-generator in version 2.2.10 does also not support the Quarkus LTS branch (e.g. 3.2.5.Final). At least in my test scenario, I got also a rest.client.reactive.jackson related issue. This is different from the issue “You need to add io.quarkus:quarkus-rest-client-reactive-jackson to your dependencies.” even though it’s present #499 but maybe someone else can verify that. So we can cover it in another issue.

[hbelmiro]

Thank you @chberger.
I just left a comment regarding a typo.

[chberger]

@hbelmiro: IMHO we must not backport this fix into the quarkus2 branch. Reason for that is the way how we detect jackson-reactive-client for quarkus2. There we use dependencies instead of capabilities:

https://github.com/quarkiverse/quarkus-openapi-generator/blob/quarkus2/deployment/src/main/java/io/quarkiverse/openapi/generator/deployment/codegen/OpenApiGeneratorCodeGenBase.java#L152