[HttpKernel] Add parameters kernel.runtime_mode and `kernel.runtime…

…_mode.*`, all set from env var `APP_RUNTIME_MODE`

Response.php

@@ -433,7 +433,7 @@ public function send(/* bool $flush = true */): static
             fastcgi_finish_request();
         } elseif (\function_exists('litespeed_finish_request')) {
             litespeed_finish_request();
-        } elseif (!\in_array(\PHP_SAPI, ['cli', 'phpdbg'], true)) {
+        } elseif (!\in_array(\PHP_SAPI, ['cli', 'phpdbg', 'embed'], true)) {
             static::closeOutputBuffers(0, true);
             flush();
         }