Reduce album art flickering in media player UI (#10163)

* Add HTTP cache header to proxied media player images

With the resource actually being cacheable, preemptively extend the cache
buster key to prevent hash collisions.

While at it, change the hash from md5 to sha256 for consistency with the
access_token method.

* Remove lint

homeassistant/components/media_player/__init__.py

@@ -12,7 +12,7 @@ import logging
 import os
 from random import SystemRandom
 
-from aiohttp import web
+from aiohttp import web, hdrs
 import async_timeout
 import voluptuous as vol
 
@@ -490,9 +490,8 @@ class MediaPlayerDevice(Entity):
     def media_image_hash(self):
         """Hash value for media image."""
         url = self.media_image_url
-
         if url is not None:
-            return hashlib.md5(url.encode('utf-8')).hexdigest()[:5]
+            return hashlib.sha256(url.encode('utf-8')).hexdigest()[:16]
 
         return None
 
@@ -966,4 +965,8 @@ class MediaPlayerImageView(HomeAssistantView):
         if data is None:
             return web.Response(status=500)
 
-        return web.Response(body=data, content_type=content_type)
+        headers = {hdrs.CACHE_CONTROL: 'max-age=3600'}
+        return web.Response(
+            body=data,
+            content_type=content_type,
+            headers=headers)