feat(admin-sdk,admin-bundler,admin-shared,medusa): Restructure admin packages (#8988)

**What**
- Renames /admin-next -> /admin
- Renames @medusajs/admin-sdk -> @medusajs/admin-bundler
- Creates a new package called @medusajs/admin-sdk that will hold all tooling relevant to creating admin extensions. This is currently `defineRouteConfig` and `defineWidgetConfig`, but will eventually also export methods for adding custom fields, register translation, etc. 
  - cc: @shahednasser we should update the examples in the docs so these functions are imported from `@medusajs/admin-sdk`. People will also need to install the package in their project, as it's no longer a transient dependency.
  - cc: @olivermrbl we might want to publish a changelog when this is merged, as it is a breaking change, and will require people to import the `defineXConfig` from the new package instead of `@medusajs/admin-shared`.
- Updates CODEOWNERS so /admin packages does not require a review from the UI team.

.eslintrc.js

@@ -81,10 +81,11 @@ module.exports = {
         project: [
           "./packages/medusa/tsconfig.json",
 
-          "./packages/admin-next/dashboard/tsconfig.json",
-          "./packages/admin-next/admin-sdk/tsconfig.json",
-          "./packages/admin-next/admin-shared/tsconfig.json",
-          "./packages/admin-next/admin-vite-plugin/tsconfig.json",
+          "./packages/admin/dashboard/tsconfig.json",
+          "./packages/admin/admin-sdk/tsconfig.json",
+          "./packages/admin/admin-shared/tsconfig.json",
+          "./packages/admin/admin-bundler/tsconfig.json",
+          "./packages/admin/admin-vite-plugin/tsconfig.json",
 
           "./packages/cli/create-medusa-app/tsconfig.json",
           "./packages/cli/medusa-cli/tsconfig.spec.json",
@@ -218,8 +219,8 @@ module.exports = {
     },
     {
       files: [
-        "packages/admin-next/dashboard/**/*.ts",
-        "packages/admin-next/dashboard/**/*.tsx",
+        "packages/admin/dashboard/**/*.ts",
+        "packages/admin/dashboard/**/*.tsx",
       ],
       plugins: ["unused-imports", "react-refresh"],
       extends: [
@@ -234,56 +235,7 @@ module.exports = {
         },
         ecmaVersion: 2018, // Allows for the parsing of modern ECMAScript features
         sourceType: "module", // Allows for the use of imports
-        project: "./packages/admin-next/dashboard/tsconfig.json",
-      },
-      globals: {
-        __BASE__: "readonly",
-      },
-      env: {
-        browser: true,
-      },
-      rules: {
-        "prettier/prettier": "error",
-        "react/prop-types": "off",
-        "new-cap": "off",
-        "require-jsdoc": "off",
-        "valid-jsdoc": "off",
-        "react-refresh/only-export-components": [
-          "warn",
-          { allowConstantExport: true },
-        ],
-        "no-unused-expressions": "off",
-        "unused-imports/no-unused-imports": "error",
-        "unused-imports/no-unused-vars": [
-          "warn",
-          {
-            vars: "all",
-            varsIgnorePattern: "^_",
-            args: "after-used",
-            argsIgnorePattern: "^_",
-          },
-        ],
-      },
-    },
-    {
-      files: [
-        "packages/admin-next/app/**/*.ts",
-        "packages/admin-next/app/**/*.tsx",
-      ],
-      plugins: ["unused-imports", "react-refresh"],
-      extends: [
-        "plugin:react/recommended",
-        "plugin:react/jsx-runtime",
-        "plugin:react-hooks/recommended",
-      ],
-      parser: "@typescript-eslint/parser",
-      parserOptions: {
-        ecmaFeatures: {
-          jsx: true,
-        },
-        ecmaVersion: 2018, // Allows for the parsing of modern ECMAScript features
-        sourceType: "module", // Allows for the use of imports
-        project: "./packages/admin-next/app/tsconfig.json",
+        project: "./packages/admin/dashboard/tsconfig.json",
       },
       globals: {
         __BASE__: "readonly",