chore: use *.json extension for config files

For consistency and readability we're explicitly adding the .json extension to config files.

.prettierrc.json

@@ -0,0 +1,7 @@
+{
+    "endOfLine": "lf",
+    "singleQuote": false,
+    "trailingComma": "all",
+    "tabWidth": 4,
+    "semi": true
+}