Refactor icon configuration for email resource

The 'icon' property was added to the 'filament-email' configuration while 'navigation_icon' was removed from the configuration and README file. The reference to 'navigation_icon' was also updated to 'resource.icon' in EmailResource class to reflect these changes.

README.md

@@ -56,6 +56,7 @@ return [
         'model' => Email::class,
         'group' => null,
         'sort' => null,
+        'icon' => null,
         'default_sort_column' => 'created_at',
         'default_sort_direction' => 'desc',
         'datetime_format' => 'Y-m-d H:i:s',
@@ -67,7 +68,6 @@ return [
             'cc',
             'bcc',
         ],
-        'navigation_icon' => 'heroicon-o-envelope',
     ],
 
     'keep_email_for_days' => 60,

config/filament-email.php

@@ -9,6 +9,7 @@
         'model' => Email::class,
         'group' => null,
         'sort' => null,
+        'icon' => null,
         'default_sort_column' => 'created_at',
         'default_sort_direction' => 'desc',
         'datetime_format' => 'Y-m-d H:i:s',
@@ -20,7 +21,6 @@
             'cc',
             'bcc',
         ],
-        'navigation_icon' => null,
     ],
 
     'keep_email_for_days' => 60,

src/Filament/Resources/EmailResource.php

@@ -47,7 +47,7 @@ public static function getNavigationLabel(): string
 
     public static function getNavigationIcon(): string | Htmlable | null
     {
-        return config('filament-email.navigation_icon') ?? 'heroicon-o-envelope';
+        return config('filament-email.resource.icon') ?? 'heroicon-o-envelope';
     }
 
     public static function getNavigationGroup(): ?string