docs: optimise docusaurus tools and website content (#481)

* docs: add @docusaurus/theme-mermaid plugin

* chore: update .gitignore for website directory

* docs: add requirements section

* docs: merge docs to website and optimise website content creation

Author: delei

.gitignore

@@ -17,3 +17,25 @@ output/
 dependency-reduced-pom.xml
 
 /.mvn/wrapper/maven-wrapper.jar
+
+# website
+.vscode/
+website/node_modules
+website/build
+website/node_modules
+website/build
+website/.docusaurus
+website/.cache-loader
+website/.env.local
+website/.env.development.local
+website/.env.test.local
+website/.env.production.local
+website/npm-debug.log*
+website/yarn-debug.log*
+website/yarn-error.log*
+website/package-lock.json
+website/versioned_docs
+website/versioned_sidebars
+website/versions.json
+website/pnpm-lock.yaml
+website/yarn.lock