fix: findByID adjust type to null if disableErrors: true is passed (#8282)

Fixes https://github.com/payloadcms/payload/issues/8280

Now, the result type of this operation:
```ts
const post = await payload.findByID({
  collection: "posts",
  id,
  disableErrors: true
})
```
is `Post | null` instead of `Post` when `disableErrors: true` is passed

Adds test for the `disableErrors` property and docs.

test/collections-rest/int.spec.ts

@@ -1,7 +1,6 @@
-import type { Payload } from 'payload'
-
-import { randomBytes } from 'crypto'
+import { randomBytes, randomUUID } from 'crypto'
 import path from 'path'
+import { NotFound, type Payload } from 'payload'
 import { fileURLToPath } from 'url'
 
 import type { NextRESTClient } from '../helpers/NextRESTClient.js'
@@ -1519,6 +1518,17 @@ describe('collections-rest', () => {
       expect(result.errors[0].message).toStrictEqual('Something went wrong.')
     })
   })
+
+  describe('Local', () => {
+    it('findByID should throw NotFound if the doc was not found, if disableErrors: true then return null', async () => {
+      const post = await createPost()
+      const id = typeof post.id === 'string' ? randomUUID() : 999
+      await expect(payload.findByID({ collection: 'posts', id })).rejects.toBeInstanceOf(NotFound)
+      await expect(
+        payload.findByID({ collection: 'posts', id, disableErrors: true }),
+      ).resolves.toBeNull()
+    })
+  })
 })
 
 async function createPost(overrides?: Partial<Post>) {