Add config for navigation icon

[sitenzo]

Hi,

I want to have this resource as subnavigation without any icons.
My top navigation has a icon, because that is not in the config i added it.

[what-the-diff]

PR Summary 📝

• 📌 Added a new navigation_icon setting
  This change provides a new "navigation_icon" option within the 'filament-email.php' settings file. Now, it's even easier to find what you're looking for, guided by winning icons! 🏆💎

• 🗑️ Removed navigationIcon property from EmailResource class
  We've said bye-bye to the "navigationIcon" property in our EmailResource class to simplify things. Less is more, right? 😌👋

• 🎯 Introduced getNavigationIcon() method in EmailResource class
  We've baked in a new method, getNavigationIcon(), that fetches the "navigation_icon" directly from our 'filament-email.php' configuration file. Efficiency for the win! 🚀🔍

[RickDBCN]

Hi Tieme,

The tests are failing, could you fix?
If the config isn't set, can we default to the standard navigation icon? This way existing users of this package do not need to update their config.

Many thanks!

[sitenzo]

Ho @RickDBCN

I have changed the config.

Can you check the changes please?

Thanks

[sitenzo]

i was to quick with the pull request.
Now it is working and all is up to date.