Make home_assistant imported sensors internal by default (#3372)

esphome/components/homeassistant/__init__.py

@@ -1,4 +1,20 @@
 import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.const import CONF_ATTRIBUTE, CONF_ENTITY_ID, CONF_INTERNAL
 
 CODEOWNERS = ["@OttoWinter"]
 homeassistant_ns = cg.esphome_ns.namespace("homeassistant")
+
+HOME_ASSISTANT_IMPORT_SCHEMA = cv.Schema(
+    {
+        cv.Required(CONF_ENTITY_ID): cv.entity_id,
+        cv.Optional(CONF_ATTRIBUTE): cv.string,
+        cv.Optional(CONF_INTERNAL, default=True): cv.boolean,
+    }
+)
+
+
+def setup_home_assistant_entity(var, config):
+    cg.add(var.set_entity_id(config[CONF_ENTITY_ID]))
+    if CONF_ATTRIBUTE in config:
+        cg.add(var.set_attribute(config[CONF_ATTRIBUTE]))