[docs] Add joy to docs package.json

[siriwatknp]

Pointed out by @cherniavskii in #32576 (comment)

• I have followed (at least) the PR section of the contributing guide.

[mui-bot]

No bundle size changes

Generated by 🚫 dangerJS against 91ec131

[cherniavskii]

Hmm, it didn't work as I expected, since dependencies are installed automatically from top-level package.json only (not docs/package.json).

We can add @mui/joy to our package.json, but I don't like this approach since there's a high chance it'll get out of sync.

I tried this in MUI X repo and it works:

index 2e5cc5027..773d6cb24 100644
--- a/docs/babel.config.js
+++ b/docs/babel.config.js
@@ -21,6 +21,7 @@ const alias = {
   '@mui/docs': '../node_modules/@mui/monorepo/packages/mui-docs/src',
   '@mui/markdown': '../node_modules/@mui/monorepo/docs/packages/markdown',
   '@mui/monorepo': '../node_modules/@mui/monorepo',
+  '@mui/joy': '../node_modules/@mui/monorepo/packages/mui-joy/src',
   docs: '../node_modules/@mui/monorepo/docs', // TODO remove
   docsx: './',
 };

What do you think? @flaviendelangle @m4theushw @oliviertassinari

[cherniavskii]

I've opened a PR in MUI X repo to address this mui/mui-x#4854
@siriwatknp change in docs/package.json is not necessary for MUI X, but if you think it still makes sense - feel free to merge this PR