Add missing property accessors

[jeromepochat]

When generating pipeline script for withCredentials with AWS credentials binding, the result script is not correct (fields are not set):

withCredentials([<object of type com.cloudbees.jenkins.plugins.awscredentials.AmazonWebServicesCredentialsBinding>]) {
    // some block
}

Instead, it should generate something like:

withCredentials([[
    $class: 'AmazonWebServicesCredentialsBinding',
    credentialsId: '1de24f4f-2f81-433a-a900-b7fc4196f81f',
    accessKeyVariable: 'AWS_ACCESS_KEY_ID',
    secretKeyVariable: 'AWS_SECRET_ACCESS_KEY'
]])

Steps to reproduce:

1. Start a Jenkins instance with AWS Credentials plugin installed
2. Create AWS Credentials (no need for real one)
3. Create pipeline and use the script syntax page to create withCredentials step using AWS credentials binding
4. Check the generated script snippet

The following exception is logged:

2024-03-20 16:29:53.774+0000 [id=56]    WARNING o.j.p.s.d.DescribableParameter#uncoerce: failed to uncoerce com.cloudbees.jenkins.plugins.awscredentials.AmazonWebServicesCredentialsBinding@2db4c9ee
java.lang.UnsupportedOperationException: no public field ‘roleArn’ (or getter method) found in class com.cloudbees.jenkins.plugins.awscredentials.AmazonWebServicesCredentialsBinding
        at org.jenkinsci.plugins.structs.describable.DescribableParameter.getValue(DescribableParameter.java:161)
        at org.jenkinsci.plugins.structs.describable.DescribableParameter.inspect(DescribableParameter.java:142)
        at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2(DescribableModel.java:656)
        at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2_(DescribableModel.java:754)
        at org.jenkinsci.plugins.structs.describable.DescribableParameter.uncoerce(DescribableParameter.java:196)
        at org.jenkinsci.plugins.structs.describable.DescribableParameter.uncoerce(DescribableParameter.java:190)
        at org.jenkinsci.plugins.structs.describable.DescribableParameter.inspect(DescribableParameter.java:142)
        at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2(DescribableModel.java:656)
        at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2_(DescribableModel.java:754)
        at org.jenkinsci.plugins.workflow.steps.StepDescriptor.uninstantiate(StepDescriptor.java:251)
        at org.jenkinsci.plugins.workflow.cps.Snippetizer.object2Groovy(Snippetizer.java:152)
        at org.jenkinsci.plugins.workflow.cps.Snippetizer.step2Groovy(Snippetizer.java:81)
        at org.jenkinsci.plugins.workflow.cps.Snippetizer.doGenerateSnippet(Snippetizer.java:522)

This adds the missing public access method to properties.

[jeromepochat]

Closed as duplicates #238