Configure linter + prettier.

- This is based on existing expectations for TS code in Google-esc repos.
- First part of the change (we have not run any linter or formatting commands). After this changeset goes in I'll do a mass changeset push.

Fixes https://b.corp.google.com/issues/411384603

.prettierrc.json

@@ -0,0 +1,7 @@
+{
+    "semi": true,
+    "trailingComma": "all",
+    "singleQuote": true,
+    "printWidth": 80,
+    "tabWidth": 2
+}