refactor: knowledge base & articles

[RitvikSardana]

Problem:
To create one article, users must create a category and then 1 sub-category. Which adds a lot of friction for the agents to add articles. The new Knowledge Base (KB) solves the issue.

Agent Knowledge Base: The agent side of the KB is focused on simplifying working with articles and categories. Here is a list of features:

1. Create articles without setting any category. Articles created without any category go to the "General" category.
2. CRUD operations on Article & Category.
3. On deletion of a category, all the articles from that category will move to the "General" category.
4. Move articles from one category to another. (Note each category must have at least one article, to remove a category delete the category first and then move the articles from that)
5. Merge Categories: if you want to merge 2 categories, click on the merge button and select the destination category. The source category will be deleted and all the articles from the source category will move to the target category.
6. Copy public links for Articles & Categories.
7. Bulk Actions: Bulk actions to move articles to a category & delete articles.

Agent.KB.2.mov

Customer Knowledge Base: The customer side of the KB is focused on finding the relevant articles quickly and having easy navigation to find the articles with ease.

Customer.KB.mov

What changed?

1. UI of the whole KB agent and customer side.
2. No Sub-categories.
3. One level of nesting: Category => Articles.
4. Patch for creating a general category & shifting all the articles without a category into the general category, and if no articles are found without a category then create one article.
5. HD Category Article DocType is not a tree doctype anymore, it is just a normal doctype.
6. HD Article DocType: Removed fields like subtitle and image.
7. Removed 39 files (half of them were dead code and the other half was of KB which were replaced by the new KB).
8. Removed 3 Unused Child Doctype: HD Team Item, HD Article Sub Category Item, HD Article Item.
9. Telemetry Events

• Agent Portal

1. kb_agent_page_viewed ⇒ category_created ⇒ article_created ⇒ article_updated
2. kb_agent_page_viewed ⇒ article_created ⇒ article_updated

• Customer Portal

1. kb_customer_page_viewed ⇒ kb_customer_page_articles ⇒ article_viewed
2. kb_customer_page_viewed ⇒ kb_customer_search_article_clicked ⇒ article_viewed