[0.8.3] Feature/Custom components into shift-next config

[jameskirkby]

This PR allows custom components to be passed to shift-next through the shiftNextConfig.set() function, for example:

shiftNextConfig.set({
  ...
  customTemplateComponents: {
    hero: Hero,
    top_level_categories: TopLevelCategories,
    sixty_forty: SixtyForty,
    article_body_quote: ArticleBodyQuote,
    article_hero: ArticleHero,
    article_headings: ArticleHeadings,
    article_body: ArticleBody,
    article_image: ArticleImage,
    article_double_image: ArticleDoubleImage,
    article_products: ArticleProducts,
    article_button: ArticleButton,
    share_bar: ShareBar,
    related_articles: ArticleRelatedArticles
  }
})

This means that the components don't need to go through shift-react-components, as this was causing issues where the custom components weren't showing in the shift-react-components Config, which meant that custom components weren't showing on the page

Also, small refactor to the renderComponents() function in shift-next to use a .map() instead of a forloop

Added some basic documentation too

[Azfletch]

👍

[hubertpompecki]

With this change in place shift-react-components can now export the templateComponentManifest directly instead of exporting buildTemplateComponentsManifest . The reason the manifest was exported as a function was so that the call to config would happen at runtime.

[jameskirkby]

I'll make a ticket for this

[hubertpompecki]

Nothing against this change in principle but I am surprised that it's needed in the first place. I thought we recently looked at adding template components and verified that it worked OK?

[jameskirkby]

@hubertpompecki it worked, then it stopped working for a reason I couldn't figure out. A couple of us looked into it and got nowhere

Feels a bit long to do this too:
next front-end -> shift-react-components -> shift-next -> next front-end

When instead, this PR does this:
next front-end -> shift-next -> next front-end