Add support for matrix keypads (#4241)

Co-authored-by: Samuel Sieb <samuel@sieb.net>

esphome/components/key_provider/key_provider.cpp

@@ -0,0 +1,13 @@
+#include "key_provider.h"
+
+namespace esphome {
+namespace key_provider {
+
+void KeyProvider::add_on_key_callback(std::function<void(uint8_t)> &&callback) {
+  this->key_callback_.add(std::move(callback));
+}
+
+void KeyProvider::send_key_(uint8_t key) { this->key_callback_.call(key); }
+
+}  // namespace key_provider
+}  // namespace esphome