Fix #354 Update contributor guide: s/json/yaml/, extension adoc page

[ppalaga]

No description provided.

[ppalaga]

@dhartford now that you freshly passed the journey, do you have any suggestions how we could further improve the Contributor guide?

[asf-ci]

Refer to this link for build results (access rights to CI server needed):
https://builds.apache.org/job/camel-quarkus-pr/366/

[dhartford]

@ppalaga The only two areas I can think of would be:

1. Reference how to safely git rebase/squash commits before a PR. There are a lot of references on the internet, however not all are made equal as I found out.

2. A starter-guide for how to identify classes that need special reflection handling for GraalVM/native builds. I know that isn't necessarily camel-specific, but likely to have a lot of experienced java developers that want to contribute that will be in the dark with that item.

I appreciate the addition to the contributor guide for mvn validate -Plicense,sourcecheck -Dcheckstyle.failOnViolation=true

[dhartford]

Cross-check: For all the references for -Pnative, do you mean -Dnative? I just tested and there aren't any native profiles yet, just the native flag for activation.

[ppalaga]

Cross-check: For all the references for -Pnative, do you mean -Dnative? I just tested and there aren't any native profiles yet, just the native flag for activation.

Good catch, thanks, the profile is called native-image let me fix it.

[ppalaga]

Ups, this got merged before I fixed the issue reported by @dhartford . Let me send a followup PR.