Add Mutiny support to JaxRS

[lizzyTheLizard]

As described in #18388 I ported the useMutiny-Feature from kotlin-server to the Jax-RS generator. Mutiny is especially useful for Quarkus as it is the default async framework. This change will not have any effect on other libraries than Quarkus and by default will be switched off.

I adapted the tests, documentation and samples as good as I could. However, the sample does not work due to #7994. I might work on that bug in the foreseeable future, but I did not want to include it into this PR.

I would be glad if @bbdouglas, @sreeshas, @jfiala, @lukoyanov, @cbornet, @jeff9finger, @karismann, @Zomzog, @lwlee2608 or @martin-mfg could have a look

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[wing328]

lgtm. thanks for the PR

[wing328]

can you please PM me via Slack when you've time?

https://join.slack.com/t/openapi-generator/shared_invite/zt-12jxxd7p2-XUeQM~4pzsU9x~eGLQqX2g