Improve WiFi reliability, especially on esp32-idf

That is, mystrom devices. BSS transition turned out to cause
issues (as Unifi was suggesting) when not client-supported.

templates/mystrom.yaml

@@ -27,6 +27,10 @@ packages:
 
 logger:
 
+wifi:
+  # BSS Transition Management support which we have enabled in APs.
+  enable_btm: true
+
 i2c:
   sda: 22
   scl: 19

templates/wifi.yaml

@@ -20,4 +20,7 @@ text_sensor:
 wifi:
   ssid: !secret wifi_ssid
   password: !secret wifi_password
+  # Used for uploading, and our DNS server understands unqualified queries.
   domain: ""
+  # Require reliable WiFi connection for IoT.
+  power_save_mode: none