fix: expose field admin main position typing

docs/fields/overview.mdx

@@ -609,7 +609,7 @@ The following options are available:
 | **`condition`**         | Programmatically show / hide fields based on other fields. [More details](#conditional-logic).                                                                                                                                   |
 | **`components`**        | All Field Components can be swapped out for [Custom Components](../custom-components/overview) that you define.                                                                                                                  |
 | **`description`**       | Helper text to display alongside the field to provide more information for the editor. [More details](#description).                                                                                                             |
-| **`position`**          | Specify if the field should be rendered in the sidebar by defining `position: 'sidebar'`.                                                                                                                                        |
+| **`position`**          | Use `'sidebar'` to render the field in the sidebar or `'main'` (default) to keep it in the main area.                                                                                                                            |
 | **`width`**             | Restrict the width of a field. You can pass any string-based value here, be it pixels, percentages, etc. This property is especially useful when fields are nested within a `Row` type where they can be organized horizontally. |
 | **`style`**             | [CSS Properties](https://developer.mozilla.org/en-US/docs/Web/CSS) to inject into the root element of the field.                                                                                                                 |
 | **`className`**         | Attach a [CSS class attribute](https://developer.mozilla.org/en-US/docs/Web/CSS/Class_selectors) to the root DOM element of a field.                                                                                             |

packages/payload/src/fields/config/types.ts

@@ -340,6 +340,8 @@ export type BlocksFilterOptions<TData = any> =
     ) => BlockSlugOrString | Promise<BlockSlugOrString | true> | true)
   | BlockSlugOrString
 
+export type FieldPosition = 'main' | 'sidebar'
+
 export type FieldAdmin = {
   className?: string
   components?: {
@@ -382,7 +384,7 @@ export type FieldAdmin = {
    */
   disableListFilter?: boolean
   hidden?: boolean
-  position?: 'sidebar'
+  position?: FieldPosition
   readOnly?: boolean
   style?: CSSProperties
   width?: CSSProperties['width']
@@ -411,7 +413,7 @@ export type AdminClient = {
    */
   disableListFilter?: boolean
   hidden?: boolean
-  position?: 'sidebar'
+  position?: FieldPosition
   readOnly?: boolean
   style?: { '--field-width'?: CSSProperties['width'] } & CSSProperties
   width?: CSSProperties['width']