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/inputs/handle-input/handle-input.tsx

@@ -0,0 +1,24 @@
+import { Input, Text } from "@medusajs/ui"
+import { ComponentProps, ElementRef, forwardRef } from "react"
+
+export const HandleInput = forwardRef<
+  ElementRef<typeof Input>,
+  ComponentProps<typeof Input>
+>((props, ref) => {
+  return (
+    <div className="relative">
+      <div className="absolute inset-y-0 left-0 z-10 flex w-8 items-center justify-center border-r">
+        <Text
+          className="text-ui-fg-muted"
+          size="small"
+          leading="compact"
+          weight="plus"
+        >
+          /
+        </Text>
+      </div>
+      <Input ref={ref} {...props} className="pl-10" />
+    </div>
+  )
+})
+HandleInput.displayName = "HandleInput"

packages/admin/dashboard/src/components/inputs/handle-input/index.ts

@@ -0,0 +1 @@
+export * from "./handle-input"