fix(validation): allow non-object params to remark/rehype plugins

[aloisklink]

Remark and Rehype plugins allow having options as a non-object type, such as a string.

For instance, the official MDX docs even have an example of this:

import {compile} from '@mdx-js/mdx'
// ...
import remarkFrontmatter from 'remark-frontmatter'
// ...
const file = '# hi'
// ...
// A plugin with options:
await compile(file, {remarkPlugins: [[remarkFrontmatter, 'toml']]})

Copied from https://mdxjs.com/docs/extending-mdx/#using-plugins

This describes an official remarkjs plugin: remarkjs/remark-frontmatter, which allows passing a string (e.g. "toml") as the options arg, instead of an object.

Apparently it may also be possible for a unified plugin to have multiple option parameters (see docs), however:

• the docs explicitly discourage this, and
• I'm not sure if this applies to remark/rehype plugins, since I've never seen a remark/rehype plugin that supports this

Motivation

Docusaurus validation is too strict for remarkPlugins and rehypePlugins.

Have you read the Contributing Guidelines on pull requests?

Yes ✔️

Test Plan

I've added a test case in packages/docusaurus-utils-validation/src/__tests__/validationSchemas.test.ts

Additionally, I've also tested by doing the following:

npx create-docusaurus@latest my-website classic
cd my-website
# version 4+ is ESM only, so require() doesn't work
npm install remark-frontmatter@3
# add to docusaurus.confing.js: remarkPlugins: [[require("remark-frontmatter"), "toml"]],
vim docusaurus.config.js
# doesn't work due to 
# [ERROR] ValidationError: "remarkPlugins[0]" does not match any of the allowed types
npm start

However, once I modified the node_modules/@docusaurus/utils-validation/lib/validationSchemas.js to match this PR, npm start worked!

Related PRs

#4412 would have made this bug a lot easier to debug.

Additionally, #4412 (comment) has some discussion about whether:

docusaurus/packages/docusaurus-utils-validation/src/validationSchemas.ts

Line 24 in 4b3f568

Joi.object(),

is correct. From my research, I also agree that it's unlikely that it will work too (but I'm not certain)

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	57
🟢 Accessibility	100
🟢 Best practices	92
🟢 SEO	100
🟢 PWA	90

Lighthouse ran on https://deploy-preview-6977--docusaurus-2.netlify.app/

[Josh-Cena]

Thanks!