fix(theme): make warning a first-class admonition, and deprecate caution admonition (#9308)

website/versioned_docs/version-3.0.0-alpha.0/api/plugin-methods/README.mdx

@@ -1,6 +1,6 @@
 # Plugin Method References
 
-:::caution
+:::warning
 
 This section is a work in progress. Anchor links or even URLs are not guaranteed to be stable.
 

website/versioned_docs/version-3.0.0-alpha.0/api/plugin-methods/extend-infrastructure.mdx

@@ -33,7 +33,7 @@ module.exports = function (context, options) {
 
 Register an extra command to enhance the CLI of Docusaurus. `cli` is a [commander](https://www.npmjs.com/package/commander/v/5.1.0) object.
 
-:::caution
+:::warning
 
 The commander version matters! We use commander v5, and make sure you are referring to the right version documentation for available APIs.
 

website/versioned_docs/version-3.0.0-alpha.0/api/plugin-methods/lifecycle-apis.mdx

@@ -113,7 +113,7 @@ This function permits one to create some global plugin data that can be read fro
 
 This data becomes accessible to your client-side/theme code through the [`useGlobalData`](../../docusaurus-core.mdx#useGlobalData) and [`usePluginData`](../../docusaurus-core.mdx#usePluginData) hooks.
 
-:::caution
+:::warning
 
 Global data is... global: its size affects the loading time of all pages of your site, so try to keep it small. Prefer `createData` and page-specific data whenever possible.
 
@@ -157,7 +157,7 @@ export default function friendsPlugin(context, options) {
 
 Modifies the internal webpack config. If the return value is a JavaScript object, it will be merged into the final config using [`webpack-merge`](https://github.com/survivejs/webpack-merge). If it is a function, it will be called and receive `config` as the first argument and an `isServer` flag as the second argument.
 
-:::caution
+:::warning
 
 The API of `configureWebpack` will be modified in the future to accept an object (`configureWebpack({config, isServer, utils, content})`)