Fix documentation build problems because of MDX syntax conflicts (#30744) (#30745)

Fix documentation build problems because of MDX syntax conflicts (#30744) (#30745)

Backport #30744 by @lunny

Documentation building has encountered a problem like below. This is
because MDX syntax doesn't allow `{customPath}`, we have to use
\`{customPath}\`

```
Error: Can't render static file for pathname "/next/administration/config-cheat-sheet"
            at generateStaticFile (/workspace/gitea/gitea-docusaurus/node_modules/@docusaurus/core/lib/ssg.js:119:15)
            at runNextTicks (node:internal/process/task_queues:60:5)
            at process.processImmediate (node:internal/timers:449:9)
            at async /workspace/gitea/gitea-docusaurus/node_modules/p-map/index.js:57:22 {
          [cause]: ReferenceError: CustomPath is not defined
              at _createMdxContent (server.bundle.js:4406:106)
              at MDXContent (server.bundle.js:10745:8)
              at Uc (server.bundle.js:264171:44)
              at Xc (server.bundle.js:264173:253)
              at Z (server.bundle.js:264179:89)
              at Yc (server.bundle.js:264182:98)
              at $c (server.bundle.js:264181:140)
              at Z (server.bundle.js:264179:345)
              at Xc (server.bundle.js:264177:231)
              at Z (server.bundle.js:264179:89)
```

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>