[SalesForce] Add a custom field to an Article type for knowledge articles

While far from ideal, you could build your own add an article UI with Visualforce and store related articles as delimited ids in a text string on the article, which you then use to render in a VF sidebar widget.

I know that it was a few years ago, but here is my code snippet for future usage. I used publishArticle(articleId, flagAsNew) and editOnlineArticle(articleId, unpublish).

You can find more details on my blog here.

public with sharing class ArticlesUtils {

@AuraEnabled
public static List<Knowledge__kav> getAllArticles(){
    return [ SELECT Id, KnowledgeArticleId, Title, UrlName FROM Knowledge__kav ];
}

@AuraEnabled
public static String createNewArticleAsADraft(String title, String urlName) {

    Knowledge__kav newArticle = new Knowledge__kav();
    newArticle.Title = title;
    newArticle.UrlName = urlName;
    insert newArticle;

    return [SELECT KnowledgeArticleId FROM Knowledge__kav WHERE Id =: newArticle.Id].KnowledgeArticleId;
}

@AuraEnabled
public static void publishArticle(String recordId) { //It need to be KnowledgeArticleId
    KbManagement.PublishingService.publishArticle(recordId, true);
}

@AuraEnabled
public static String unPublishArticle(String recordId){ //It need to be KnowledgeArticleId
    String newArticleId = KbManagement.PublishingService.editOnlineArticle(recordId, true); //Method new version id use it to update 
    return [SELECT KnowledgeArticleId FROM Knowledge__kav WHERE Id =: newArticleId].KnowledgeArticleId;
}

@AuraEnabled
public static String updateDraftArticleWithoutPublish(String title, String urlName, Id recordId) {

    Knowledge__kav newArticle = [ SELECT Id, KnowledgeArticleId, Title, UrlName FROM Knowledge__kav WHERE KnowledgeArticleId =: recordId ];   

    newArticle.Title = title;
    newArticle.UrlName = urlName;

    update newArticle;

    return newArticle.KnowledgeArticleId;
}

@AuraEnabled
public static String updatetArticle(String title, String urlName, Id recordId) {

    String newVersionId = unPublishArticle(recordId);

    Knowledge__kav newArticle = [ SELECT Id, KnowledgeArticleId, Title, UrlName FROM Knowledge__kav WHERE KnowledgeArticleId =: newVersionId ];   

    newArticle.Title = title;
    newArticle.UrlName = urlName;

    update newArticle;

    publishArticle(newVersionId);

    return newVersionId;
}
}

Usage example:

List<Knowledge__kav> articles = ArticlesUtils.getAllArticles();

String newArticleKnowledgeId = ArticlesUtils.createNewArticleAsADraft('SalesforceProfs', 'salesforce-profs');

ArticlesUtils.publishArticle(newArticleKnowledgeId);

//unpublish, update, publish > separate actions
String newArticleVersionId = ArticlesUtils.unPublishArticle(newArticleKnowledgeId);
ArticlesUtils.updateDraftArticleWithoutPublish('SalesforceProfs Update', 'salesforce-profs-update', newArticleVersionId);
ArticlesUtils.publishArticle(newArticleVersionId);

//update - contain unpublish, update, publish
//ArticlesUtils.updatetArticle('SalesforceProfs Update', 'salesforce-profs-update', newArticleKnowledgeId);