[website] fix sidebar (apache#2241)

### Motivation

In apache#2237, `administration-auth` is removed. However it is not removed from sidebard. It is causing failures on building website.

```
generate.js triggered...
Error: Improper sidebars.json file, document with id 'administration-auth' not found. Make sure that documents with the ids specified in sidebars.json exist and that no ids are repeated.
    at _loop (/pulsar/site2/website/node_modules/docusaurus/lib/server/readCategories.js:58:17)
    at readCategories (/pulsar/site2/website/node_modules/docusaurus/lib/server/readCategories.js:34:53)
    at DocsSidebar.render (/pulsar/site2/website/node_modules/docusaurus/lib/core/DocsSidebar.js:16:26)
    at processChild (/pulsar/site2/website/node_modules/react-dom/cjs/react-dom-server.node.development.js:2204:18)
    at resolve (/pulsar/site2/website/node_modules/react-dom/cjs/react-dom-server.node.development.js:2061:5)
    at ReactDOMServerRenderer.render (/pulsar/site2/website/node_modules/react-dom/cjs/react-dom-server.node.development.js:2380:22)
    at ReactDOMServerRenderer.read (/pulsar/site2/website/node_modules/react-dom/cjs/react-dom-server.node.development.js:2354:19)
    at renderToStaticMarkup (/pulsar/site2/website/node_modules/react-dom/cjs/react-dom-server.node.development.js:2737:25)
    at renderToStaticMarkupWithDoctype (/pulsar/site2/website/node_modules/docusaurus/lib/server/renderUtils.js:16:30)
    at /pulsar/site2/website/node_modules/docusaurus/lib/server/generate.js:199:17
```

 ### Changes

Remove `administration-auth` from the sidebar. Also remove codebase page, which doesn't make sense to be there because code changes are happening very frequently. The page quickly becomes out-of-dated.
Additionally cleanup a few things in the sidebar.

site2/docs/adaptors-kafka.md

@@ -1,7 +1,7 @@
 ---
 id: adaptors-kafka
 title: Pulsar adaptor for Apache Kafka
-sidebar_label: Kafka client wrappter
+sidebar_label: Kafka client wrapper
 ---
 
 

site2/docs/client-libraries-websocket.md

@@ -1,7 +1,7 @@
 ---
 id: client-libraries-websocket
 title: Pulsar's WebSocket API
-sidebar_label: WebSocket API
+sidebar_label: WebSocket
 ---
 
 Pulsar's [WebSocket](https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API) API is meant to provide a simple way to interact with Pulsar using languages that do not have an official [client library](getting-started-clients.md). Through WebSockets you can publish and consume messages and use all the features available in the [Java](client-libraries-java.md), [Python](client-libraries-python.md), and [C++](client-libraries-cpp.md) client libraries.

site2/docs/cookbooks-deduplication.md

@@ -1,7 +1,7 @@
 ---
 id: cookbooks-deduplication
 title: Message deduplication
-sidebar_label: Managing message deduplication 
+sidebar_label: Message deduplication 
 ---
 
 **Message deduplication** is a feature of Pulsar that, when enabled, ensures that each message produced on Pulsar topics is persisted to disk *only once*, even if the message is produced more than once. Message deduplication essentially unburdens Pulsar applications of the responsibility of ensuring deduplication and instead handles it automatically on the server side.

site2/website/sidebars.json

@@ -30,17 +30,16 @@
     "Pulsar administration": [
       "administration-zk-bk",
       "administration-geo",
-      "administration-auth",
       "administration-dashboard",
       "administration-stats",
       "administration-load-distribution",
       "administration-proxy"
     ],
     "Security": [
       "security-overview",
+      "security-tls",
       "security-athenz",
       "security-authorization",
-      "security-tls",
       "security-encryption",
       "security-extending"
     ],