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/lib/extension-helpers.ts

@@ -0,0 +1,57 @@
+import { RouteObject } from "react-router-dom"
+import { ErrorBoundary } from "../components/utilities/error-boundary"
+
+/**
+ * Used to test if a route is a settings route.
+ */
+export const settingsRouteRegex = /^\/settings\//
+
+export const createRouteMap = (
+  routes: { path: string; Component: () => JSX.Element }[],
+  ignore?: string
+): RouteObject[] => {
+  const root: RouteObject[] = []
+
+  const addRoute = (
+    pathSegments: string[],
+    Component: () => JSX.Element,
+    currentLevel: RouteObject[]
+  ) => {
+    if (!pathSegments.length) {
+      return
+    }
+
+    const [currentSegment, ...remainingSegments] = pathSegments
+    let route = currentLevel.find((r) => r.path === currentSegment)
+
+    if (!route) {
+      route = { path: currentSegment, children: [] }
+      currentLevel.push(route)
+    }
+
+    if (remainingSegments.length === 0) {
+      route.children ||= []
+      route.children.push({
+        path: "",
+        ErrorBoundary: ErrorBoundary,
+        async lazy() {
+          return { Component }
+        },
+      })
+    } else {
+      route.children ||= []
+      addRoute(remainingSegments, Component, route.children)
+    }
+  }
+
+  routes.forEach(({ path, Component }) => {
+    // Remove the ignore segment from the path if it is provided
+    const cleanedPath = ignore
+      ? path.replace(ignore, "").replace(/^\/+/, "")
+      : path.replace(/^\/+/, "")
+    const pathSegments = cleanedPath.split("/").filter(Boolean)
+    addRoute(pathSegments, Component, root)
+  })
+
+  return root
+}