Add push-to-talk sound effects

Fixes https://github.com/vector-im/element-call/issues/296

.eslintrc.js

@@ -19,6 +19,7 @@ module.exports = {
         // We break this rule in a few places: dial it back to a warning
         // (and run with max warnings) to tolerate the existing code
         "react-hooks/exhaustive-deps": ["warn"],
+        "jsx-a11y/media-has-caption": ["off"],
     },
     overrides: [
         {