Expose web_server port via the API (#2467)

esphome/core/__init__.py

@@ -10,6 +10,7 @@ from esphome.const import (
     CONF_USE_ADDRESS,
     CONF_ETHERNET,
     CONF_WIFI,
+    CONF_PORT,
     KEY_CORE,
     KEY_TARGET_FRAMEWORK,
     KEY_TARGET_PLATFORM,
@@ -519,6 +520,19 @@ class EsphomeCore:
 
         return None
 
+    @property
+    def web_port(self) -> Optional[int]:
+        if self.config is None:
+            raise ValueError("Config has not been loaded yet")
+
+        if "web_server" in self.config:
+            try:
+                return self.config["web_server"][CONF_PORT]
+            except KeyError:
+                return 80
+
+        return None
+
     @property
     def comment(self) -> Optional[str]:
         if self.config is None: