Migrate to Next.js

[jakeburden]

Preview URL:

https://next-docs.amplify.aws/

Description of changes:

• Moved away from using Capi/Stencil as our docs build system.
• Moved to using Next.js and React, utilizing continuously improving open source tools.
• By utilizing React + Next.js, we also enable more contributions, a faster development feedback loop, and more feature-rich improvements to the site.
• Docs markdown is now parsed with MDX - meaning you can use React components in markdown files.
• As Amplify Console natively supports Next.js Server-Side Rendering (SSR), we’ll be able to leverage our own product to add more advancements to the docs site such as internationalization (i18N) and image optimization.
• By utilizing Next.js/MDX we can fine-tune and have greater control over meta information parsed by search engines to help with SEO ranking. We can do this by passing SEO friendly meta-data to the next/head component. Since all content is static generated (and SSR in the future), search engines will be able to parse all content immediately.
• Next.js enables us to choose which pages will be statically generated for speed and performance, and which pages will be server-side generated to provide more feature-rich experiences that require a sever runtime.

The content authoring experience should remain mostly the same, with three key differences:

1. Rather than using <inline-fragment> we now use <Fragments>, and those fragments live in the /src/fragments directory.
   Example:

   import js from "/src/fragments/lib/datastore/js/conflict.mdx";
   
   <Fragments fragments={{js: js}} />;

2. Rather than using <amplify-block> and <amplify-block-switcher> we now use <Block> and <BlockSwitcher>
   Example:

   <BlockSwitcher>
   
   <Block name="JavaScript">
   
   ```js
   const a = "a";
   ```
   
   </Block>
   
   <Block name="TypeScript">
   
   ```ts
   const a: "a" = "a";
   ```
   
   </Block>
   
   <Block name="Rust">
   
   ```rust
   let mut a = String::from("a");
   ```
   
   </Block>
   
   </BlockSwitcher>

3. Rather than using <ui-component-props>, we now use <UiComponentProps>
   Example:
   <UiComponentProps tag="amplify-s3-image" propType="attr" useTableHeaders />

[lgtm-com]

This pull request introduces 5 alerts when merging 52c986b into 373be37 - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class
• 1 for Useless assignment to local variable
• 1 for Useless conditional
• 1 for String instead of regular expression

[lgtm-com]

This pull request introduces 5 alerts when merging 128ca04 into 373be37 - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class
• 1 for Useless assignment to local variable
• 1 for Useless conditional
• 1 for String instead of regular expression

[lgtm-com]

This pull request introduces 5 alerts when merging 9cf51ef into 373be37 - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class
• 1 for Useless assignment to local variable
• 1 for Useless conditional
• 1 for String instead of regular expression

[mauerbac]

Reviewed offline. Approved

[lgtm-com]

This pull request introduces 3 alerts when merging 04f9ac6 into 373be37 - view on LGTM.com

new alerts:

• 1 for Useless assignment to local variable
• 1 for Useless conditional
• 1 for String instead of regular expression