Add select entities and implement template select (#2067)

Co-authored-by: Otto Winter <otto@otto-winter.com>

esphome/components/mqtt/mqtt_select.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include "esphome/core/defines.h"
+
+#ifdef USE_SELECT
+
+#include "esphome/components/select/select.h"
+#include "mqtt_component.h"
+
+namespace esphome {
+namespace mqtt {
+
+class MQTTSelectComponent : public mqtt::MQTTComponent {
+ public:
+  /** Construct this MQTTSelectComponent instance with the provided friendly_name and select
+   *
+   * @param select The select.
+   */
+  explicit MQTTSelectComponent(select::Select *select);
+
+  // ========== 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 is_internal() override;
+
+  bool publish_state(const std::string &value);
+
+ protected:
+  /// Override for MQTTComponent, returns "select".
+  std::string component_type() const override;
+
+  std::string friendly_name() const override;
+
+  select::Select *select_;
+};
+
+}  // namespace mqtt
+}  // namespace esphome
+
+#endif