fix(db-postgres): joins to self collection (#10182)

### What?
With Postgres, before join to self like:
```ts
import type { CollectionConfig } from 'payload'

export const SelfJoins: CollectionConfig = {
  slug: 'self-joins',
  fields: [
    {
      name: 'rel',
      type: 'relationship',
      relationTo: 'self-joins',
    },
    {
      name: 'joins',
      type: 'join',
      on: 'rel',
      collection: 'self-joins',
    },
  ],
}
```
wasn't possible, even though it's a valid usage.

### How?
Now, to differentiate parent `self_joins` and children `self_joins` we
do additional alias for the nested select -
`"4d3cf2b6_1adf_46a8_b6d2_3e1c3809d737"`:
```sql
select 
  "id", 
  "rel_id", 
  "updated_at", 
  "created_at", 
  (
    select 
      coalesce(
        json_agg(
          json_build_object('id', "joins_alias".id)
        ), 
        '[]' :: json
      ) 
    from 
      (
        select 
          "created_at", 
          "rel_id", 
          "id" 
        from 
          "self_joins" "4d3cf2b6_1adf_46a8_b6d2_3e1c3809d737" 
        where 
          "4d3cf2b6_1adf_46a8_b6d2_3e1c3809d737"."rel_id" = "self_joins"."id" 
        order by 
          "4d3cf2b6_1adf_46a8_b6d2_3e1c3809d737"."created_at" desc 
        limit 
          $1
      ) "joins_alias"
  ) as "joins_alias" 
from 
  "self_joins" 
where 
  "self_joins"."id" = $2 
order by 
  "self_joins"."created_at" desc 
limit 
  $3

```

Fixes https://github.com/payloadcms/payload/issues/10144

-->

test/joins/collections/SelfJoins.ts

@@ -0,0 +1,18 @@
+import type { CollectionConfig } from 'payload'
+
+export const SelfJoins: CollectionConfig = {
+  slug: 'self-joins',
+  fields: [
+    {
+      name: 'rel',
+      type: 'relationship',
+      relationTo: 'self-joins',
+    },
+    {
+      name: 'joins',
+      type: 'join',
+      on: 'rel',
+      collection: 'self-joins',
+    },
+  ],
+}

test/joins/config.ts

@@ -6,6 +6,7 @@ import { Categories } from './collections/Categories.js'
 import { CategoriesVersions } from './collections/CategoriesVersions.js'
 import { HiddenPosts } from './collections/HiddenPosts.js'
 import { Posts } from './collections/Posts.js'
+import { SelfJoins } from './collections/SelfJoins.js'
 import { Singular } from './collections/Singular.js'
 import { Uploads } from './collections/Uploads.js'
 import { Versions } from './collections/Versions.js'
@@ -37,6 +38,7 @@ export default buildConfigWithDefaults({
     Versions,
     CategoriesVersions,
     Singular,
+    SelfJoins,
     {
       slug: localizedPostsSlug,
       admin: {

test/joins/int.spec.ts

@@ -1,4 +1,4 @@
-import type { Payload } from 'payload'
+import type { Payload, TypeWithID } from 'payload'
 
 import path from 'path'
 import { getFileByPath } from 'payload'
@@ -975,6 +975,15 @@ describe('Joins Field', () => {
 
     await payload.delete({ collection: categoriesSlug, where: { name: { equals: 'totalDocs' } } })
   })
+
+  it('should self join', async () => {
+    const doc_1 = await payload.create({ collection: 'self-joins', data: {} })
+    const doc_2 = await payload.create({ collection: 'self-joins', data: { rel: doc_1 }, depth: 0 })
+
+    const data = await payload.findByID({ collection: 'self-joins', id: doc_1.id, depth: 1 })
+
+    expect((data.joins.docs[0] as TypeWithID).id).toBe(doc_2.id)
+  })
 })
 
 async function createPost(overrides?: Partial<Post>, locale?: Config['locale']) {

test/joins/payload-types.ts

@@ -18,6 +18,7 @@ export interface Config {
     versions: Version;
     'categories-versions': CategoriesVersion;
     singular: Singular;
+    'self-joins': SelfJoin;
     'localized-posts': LocalizedPost;
     'localized-categories': LocalizedCategory;
     'restricted-categories': RestrictedCategory;
@@ -53,6 +54,9 @@ export interface Config {
       relatedVersions: 'versions';
       relatedVersionsMany: 'versions';
     };
+    'self-joins': {
+      joins: 'self-joins';
+    };
     'localized-categories': {
       relatedPosts: 'localized-posts';
     };
@@ -71,6 +75,7 @@ export interface Config {
     versions: VersionsSelect<false> | VersionsSelect<true>;
     'categories-versions': CategoriesVersionsSelect<false> | CategoriesVersionsSelect<true>;
     singular: SingularSelect<false> | SingularSelect<true>;
+    'self-joins': SelfJoinsSelect<false> | SelfJoinsSelect<true>;
     'localized-posts': LocalizedPostsSelect<false> | LocalizedPostsSelect<true>;
     'localized-categories': LocalizedCategoriesSelect<false> | LocalizedCategoriesSelect<true>;
     'restricted-categories': RestrictedCategoriesSelect<false> | RestrictedCategoriesSelect<true>;
@@ -355,6 +360,20 @@ export interface CategoriesVersion {
   createdAt: string;
   _status?: ('draft' | 'published') | null;
 }
+/**
+ * This interface was referenced by `Config`'s JSON-Schema
+ * via the `definition` "self-joins".
+ */
+export interface SelfJoin {
+  id: string;
+  rel?: (string | null) | SelfJoin;
+  joins?: {
+    docs?: (string | SelfJoin)[] | null;
+    hasNextPage?: boolean | null;
+  } | null;
+  updatedAt: string;
+  createdAt: string;
+}
 /**
  * This interface was referenced by `Config`'s JSON-Schema
  * via the `definition` "localized-posts".
@@ -467,6 +486,10 @@ export interface PayloadLockedDocument {
         relationTo: 'singular';
         value: string | Singular;
       } | null)
+    | ({
+        relationTo: 'self-joins';
+        value: string | SelfJoin;
+      } | null)
     | ({
         relationTo: 'localized-posts';
         value: string | LocalizedPost;
@@ -666,6 +689,16 @@ export interface SingularSelect<T extends boolean = true> {
   updatedAt?: T;
   createdAt?: T;
 }
+/**
+ * This interface was referenced by `Config`'s JSON-Schema
+ * via the `definition` "self-joins_select".
+ */
+export interface SelfJoinsSelect<T extends boolean = true> {
+  rel?: T;
+  joins?: T;
+  updatedAt?: T;
+  createdAt?: T;
+}
 /**
  * This interface was referenced by `Config`'s JSON-Schema
  * via the `definition` "localized-posts_select".