docs: translate gitlab-ops to en-gb, enhance gravatar article, fix heading levels

- Translate GitLab Operations article from Chinese to British English
- Add comprehensive Gravatar usage guide with code examples in both locales
- Fix heading levels on notification pages (h1 -> h2)
- Enable line numbers in code blocks via rspress config

rspress.config.ts

@@ -18,6 +18,9 @@ export default defineConfig({
       },
     ],
   },
+  markdown: {
+    showLineNumbers: true
+  },
   lang: "en-gb",
   locales: [
     {