If you want to add Jenkins S3 plugin (or any other plugin) to your Jenkins Configuration as Code deployment you may hit a problem that the plugin cannot be configured easily using YAML.

In such case you can go with groovy init script. Just add them to your values.yaml, for example:

# List of groovy init scripts to be executed during Jenkins master start
initScripts:
#  - |
#    print 'adding global pipeline libraries, register properties, bootstrap jobs...'
  s3: |
    import jenkins.model.*
    import hudson.plugins.s3.*

    instance  = Jenkins.instance
    new_name  = "s3"
    accessKey = "access"
    secretKey = "secret"
    useRole   = false
    S3Profile profile = new S3Profile(new_name, accessKey, secretKey, useRole, 60, "", "", "", "", false);

    publisher = hudson.plugins.s3.S3BucketPublisher
    des       = new hudson.plugins.s3.S3BucketPublisher.DescriptorImpl();
    s3Plugin  = instance.getDescriptor(S3BucketPublisher.class);

    new_profiles = [];
    des.getProfiles().each { if (it.name != new_name) { new_profiles.push(it) } }
    new_profiles.push(profile)

Follow ups:

https://issues.jenkins-ci.org/browse/JENKINS-55595

https://github.com/jenkinsci/s3-plugin/pull/118