feat: add icelandic translations (#13423)

### What?

Add Icelandic translations

### Why?

It hadn't been implemented yet

### How?

I added files, mimicking the existing pattern for translations and
translated all messages in the list

Author: jonnigs

packages/payload/src/exports/i18n/is.ts

@@ -0,0 +1 @@
+export { is } from '@payloadcms/translations/languages/is'

packages/translations/src/exports/all.ts

@@ -19,6 +19,7 @@ import { hr } from '../languages/hr.js'
 import { hu } from '../languages/hu.js'
 import { hy } from '../languages/hy.js'
 import { id } from '../languages/id.js'
+import { is } from '../languages/is.js'
 import { it } from '../languages/it.js'
 import { ja } from '../languages/ja.js'
 import { ko } from '../languages/ko.js'
@@ -64,6 +65,7 @@ export const translations = {
   hy,
 
   id,
+  is,
   it,
   ja,
   ko,

packages/translations/src/importDateFNSLocale.ts

@@ -76,6 +76,12 @@ export const importDateFNSLocale = async (locale: string): Promise<Locale> => {
       result = (await import('date-fns/locale/id')).id
 
       break
+
+    case 'is':
+      result = (await import('date-fns/locale/is')).is
+
+      break
+
     case 'it':
       result = (await import('date-fns/locale/it')).it