Add datetime date entities (#6191)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/mqtt/mqtt_date.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include "esphome/core/defines.h"
+
+#ifdef USE_MQTT
+#ifdef USE_DATETIME_DATE
+
+#include "esphome/components/datetime/date_entity.h"
+#include "mqtt_component.h"
+
+namespace esphome {
+namespace mqtt {
+
+class MQTTDateComponent : public mqtt::MQTTComponent {
+ public:
+  /** Construct this MQTTDatetimeComponent instance with the provided friendly_name and datetime
+   *
+   * @param datetime The datetime component.
+   */
+  explicit MQTTDateComponent(datetime::DateEntity *date);
+
+  // ========== INTERNAL METHODS ==========
+  // (In most use cases you won't need these)
+  /// Override setup.
+  void setup() override;
+  void dump_config() override;
+
+  void send_discovery(JsonObject root, mqtt::SendDiscoveryConfig &config) override;
+
+  bool send_initial_state() override;
+
+  bool publish_state(uint16_t year, uint8_t month, uint8_t day);
+
+ protected:
+  std::string component_type() const override;
+  const EntityBase *get_entity() const override;
+
+  datetime::DateEntity *date_;
+};
+
+}  // namespace mqtt
+}  // namespace esphome
+
+#endif  // USE_DATETIME_DATE
+#endif  // USE_MQTT