Allow prefilling with comments on investigation and study level via config

[patrick-koenig]

Two examples, one for investigation and one for study level:

    prefill: [
        {
            type: 'comment',
            isaMapping: {
                entity: 'investigation',
                attribute: 'comments'
            },
            values: {
                name: 'Study Country',
                value: 'Germany'
            }
        },
        {
            type: 'comment',
            isaMapping: {
                entity: 'study',
                attribute: 'comments',
                studyIndex: 0
            },
            values: {
                name: 'Study Country',
                value: 'Germany'
            }
        }
    ],