Migrate components including ApiLink for the Documentation content (#6120)

Motivation:

- Background: #6098
- I am starting the migration with the Documentation menu, as its
content is the least dynamic.

Modifications:

- Implement remark plugin for api link.
- Implement `AspectRatio`, `ApiLink` components.
- Use the built-in `CodeBlock` component and add language support.
- Register components to global scope to use them in every MDX file
without importing.
- Add a CLI option for not opening the browser on start.
- Remove auto generated initial docs.

Result:

- Api link syntax in MDX has changed from `<type://RequestContext>` to
`[RequestContext](type)`. See
[`site-new/docs/api-link-test.mdx`](https://github.com/line/armeria/pull/6120/files#diff-d5c8d81e39c3c962d2a78ba84c7624842e1826c8c3e751eacb9c792cf62b51dd)
for usages. I made this change because the old syntax is no longer
allowed in MDX v3. (See [MDX
docs](https://mdxjs.com/docs/troubleshooting-mdx/#unexpected-character-at-expected-expect))

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Meri Kim <dl_armeria@linecorp.com>

Author: 3 people

site-new/docs/api-link-test.mdx

@@ -0,0 +1,24 @@
+---
+sidebar_position: 3
+---
+
+# API Link Samples
+
+## Type
+
+- [RequestContext](type)
+- [@Get](type)
+- [@Post](type)
+
+## Type with expressions
+
+- [RequestContext#attrs()](type):
+- [RequestContext#attr(AttributeKey)](type):
+- [WebClient#execute(HttpRequest,RequestOptions)?full](type)
+
+## Type on title: [WebClientRequestPreparation](type)
+
+## Plural
+
+- [Request](typeplural)
+- [AccessLogWriter](typeplural)

site-new/docs/index.mdx

@@ -0,0 +1,83 @@
+---
+sidebar_position: 1
+---
+
+# User manual
+
+## What is Armeria?
+
+_Armeria_ is your go-to microservice framework for any situation. You can build any type of
+microservice leveraging your favorite technologies, including [gRPC](https://grpc.io/),
+[Thrift](https://thrift.apache.org/), [Kotlin](https://kotlinlang.org/),
+[Retrofit](https://square.github.io/retrofit/), [Reactive Streams](https://www.reactive-streams.org/),
+[Spring Boot](https://spring.io/projects/spring-boot) and [Dropwizard](https://www.dropwizard.io/).
+
+It is open-sourced by the creator of [Netty](https://netty.io/) and his colleagues at
+[LY Corporation](https://techblog.lycorp.co.jp/en).
+
+## Want a quick tour?
+
+Check out the recent introductory talk
+([slides](https://speakerdeck.com/trustin/armeria-a-microservice-framework-well-suited-everywhere)):
+
+<AspectRatio width={16} height={9} maxWidth="21rem">
+  <iframe
+    src="https://www.youtube.com/embed/Vr-0GKUmzo8"
+    style={{ border: 'none' }}
+    allowfullscreen
+  />
+</AspectRatio>
+
+## Features
+
+### HTTP/2
+
+- Supports HTTP/2 on both TLS and cleartext connections
+- Supports protocol upgrade via both HTTP/2 connection preface and traditional HTTP/1 upgrade request
+- Fully compatible with existing HTTP/1 servers
+- Integrated PROXY protocol support for interoperability with load balancers such as HAProxy and AWS ELB.
+
+### Integration with gRPC and Thrift
+
+- Your gRPC or Thrift service implementation runs on top of Armeria without any modification.
+- Works with the official gRPC or Thrift-over-HTTP client
+- Works with the code generated by the official Protobuf or Thrift IDL compiler
+- Supports various protocol combinations, such as:
+  - gRPC-over-HTTP/1 & 2
+  - Thrift-over-HTTP/1 & 2
+  - gRPC-Web
+- See [Running a Thrift service](/docs/server-thrift) and [Running a gRPC service](/docs/server-grpc).
+
+### Essential features for building microservices
+
+- Metrics
+- Circuit breaker
+- Client-side health-check and load-balancing
+- Service discovery from various sources such as DNS and ZooKeeper
+  - See [Client-side load balancing and service discovery](/docs/client-service-discovery).
+- Distributed call tracing via Zipkin
+
+### Interactive web-based debug console
+
+- Browse the list of available RPC operations
+- Invoke an RPC operation via a web form
+- Share an RPC request with your colleagues so they can reproduce the problem easily
+  - Just like sharing a cURL command, but works for RPC
+- See [Browsing and invoking services with DocService](/docs/server-docservice).
+
+### Completely asynchronous and reactive
+
+- Built on top of Reactive Streams and Java 8 CompletableFuture
+- Asynchronous connection pool ensures your application never blocks even on pool exhaustion.
+- Domain name lookups are also fully asynchronous thanks to Netty’s asynchronous domain name resolver.
+
+### Compatibility with existing Java EE web applications
+
+- Runs any Java EE web applications such as Spring Boot on the same TCP/IP port
+- Your Java EE web application speaks HTTP/2!
+- See [Embedding a servlet container](/docs/server-servlet).
+
+### Even higher performance on Linux
+
+- JNI-based socket I/O
+- BoringSSL-based TLS connections