fix(java17): add Jackson converter to RestAdapters to avoid Gson (backport #1174)

[mergify]

This is an automatic backport of pull request #1174 done by Mergify.
Cherry-pick of c1bd0b1 has failed:

On branch mergify/bp/release-1.32.x/pr-1174
Your branch is up to date with 'origin/release-1.32.x'.

You are currently cherry-picking commit c1bd0b19.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   igor-web/src/main/groovy/com/netflix/spinnaker/igor/config/DockerRegistryConfig.groovy
	modified:   igor-web/src/main/groovy/com/netflix/spinnaker/igor/config/EchoConfig.groovy
	modified:   igor-web/src/main/groovy/com/netflix/spinnaker/igor/config/WerckerConfig.groovy
	modified:   igor-web/src/test/groovy/com/netflix/spinnaker/igor/wercker/WerckerClientSpec.groovy

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   igor-web/src/main/groovy/com/netflix/spinnaker/igor/config/PluginMonitorConfig.java

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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