prefixPath : Generalization to other usages and Secret Parameter configuration

[lenaing]

Hello,

Thanks to #67 we can (finally !) request secrets from non-at-root mounted KVs. And that's great ! 👍

Now we can do this in a scripted pipeline :

def secrets = [
    [path: 'test/nonrootkv/secret', secretValues: [[envVar: 'result', vaultKey: 'secretkey']]]
]

def configuration = [
    vaultUrl: 'https://vault.example.com',
    prefixPath: 'test/nonrootkv/',
    vaultCredentialId: 'credentialID'
]

pipeline {
    agent {
        node {
            label 'default'
        }
    }
    stages {
        stage('Test get Secret'){
            steps {
                script {
                    withVault([configuration: configuration, vaultSecrets: secrets]) {
                        sh 'if [ -n "${result}" ]; then echo "variable is defined" && echo "test${result}"; else exit 1 ; fi'
                    }
                }
            }
        }
    }
}

However :

• This isn't documented in the README.md
• It would be nice to enable the prefixPath parameterization at many levels. On the top of my head I think about non-at-root mounted authentication endpoints. This would enable tidying of users' Vault mount points rather than requiring them to have everything mounted at the Vault root.
• The Vault Secret UI config parameter does not enable a user to set a prefixPath for a non-root KV (and fails to read such secrets) :
  

Kind regards

[jetersen]

Feel free to submit a PR your halfway there anyhow.