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.

packages/admin/dashboard/src/components/utilities/error-boundary/error-boundary.tsx

@@ -0,0 +1,65 @@
+import { ExclamationCircle } from "@medusajs/icons"
+import { Text } from "@medusajs/ui"
+import { useTranslation } from "react-i18next"
+import { Navigate, useLocation, useRouteError } from "react-router-dom"
+
+import { isFetchError } from "../../../lib/is-fetch-error"
+
+export const ErrorBoundary = () => {
+  const error = useRouteError()
+  const location = useLocation()
+  const { t } = useTranslation()
+
+  let code: number | null = null
+
+  if (isFetchError(error)) {
+    if (error.status === 401) {
+      return <Navigate to="/login" state={{ from: location }} replace />
+    }
+
+    code = error.status ?? null
+  }
+
+  let title: string
+  let message: string
+
+  switch (code) {
+    case 400:
+      title = t("errorBoundary.badRequestTitle")
+      message = t("errorBoundary.badRequestMessage")
+      break
+    case 404:
+      title = t("errorBoundary.notFoundTitle")
+      message = t("errorBoundary.notFoundMessage")
+      break
+    case 500:
+      title = t("errorBoundary.internalServerErrorTitle")
+      message = t("errorBoundary.internalServerErrorMessage")
+      break
+    default:
+      title = t("errorBoundary.defaultTitle")
+      message = t("errorBoundary.defaultMessage")
+      break
+  }
+
+  return (
+    <div className="flex size-full min-h-[calc(100vh-57px-24px)] items-center justify-center">
+      <div className="flex flex-col gap-y-6">
+        <div className="text-ui-fg-subtle flex flex-col items-center gap-y-3">
+          <ExclamationCircle />
+          <div className="flex flex-col items-center justify-center gap-y-1">
+            <Text size="small" leading="compact" weight="plus">
+              {title}
+            </Text>
+            <Text
+              size="small"
+              className="text-ui-fg-muted text-balance text-center"
+            >
+              {message}
+            </Text>
+          </div>
+        </div>
+      </div>
+    </div>
+  )
+}

packages/admin/dashboard/src/components/utilities/error-boundary/index.ts

@@ -0,0 +1 @@
+export { ErrorBoundary } from "./error-boundary"