Feat config cluster

[gaetan-hexadog]

Add the possibility to configure a cluster for the EmailResource

[what-the-diff]

PR Summary 📚

• Addition of 'cluster' Parameter to Configuration File 🎯
  This change introduces a new option called 'cluster' in our configuration settings. Think of 'cluster' as a new preference knob you can adjust to further customize your experience. The change took place in a setting book called 'config/filament-email.php'.

• Introduction of 'getCluster()' Method 🎩
  A fresh feature called 'getCluster()' has been introduced. It's like having a new magic trick up our sleeve! This one can help us understand and manage the 'cluster' setting we discussed above. This new trick lives in our magic toolkit named 'src/Filament/Resources/EmailResource.php' file.

[RickDBCN]

Thanks!