Add support for fan preset modes (#5694)

Co-authored-by: J. Nick Koston <nick@koston.org>

esphome/components/fan/fan_traits.h

@@ -1,3 +1,6 @@
+#include <set>
+#include <utility>
+
 #pragma once
 
 namespace esphome {
@@ -25,12 +28,19 @@ class FanTraits {
   bool supports_direction() const { return this->direction_; }
   /// Set whether this fan supports changing direction
   void set_direction(bool direction) { this->direction_ = direction; }
+  /// Return the preset modes supported by the fan.
+  std::set<std::string> supported_preset_modes() const { return this->preset_modes_; }
+  /// Set the preset modes supported by the fan.
+  void set_supported_preset_modes(const std::set<std::string> &preset_modes) { this->preset_modes_ = preset_modes; }
+  /// Return if preset modes are supported
+  bool supports_preset_modes() const { return !this->preset_modes_.empty(); }
 
  protected:
   bool oscillation_{false};
   bool speed_{false};
   bool direction_{false};
   int speed_count_{};
+  std::set<std::string> preset_modes_{};
 };
 
 }  // namespace fan