feat(@typescript-eslint): enable switch-exhaustiveness-check

It's a no-brainer given we have `default-case` enabled

Author: G-Rath

@typescript-eslint.js

@@ -103,6 +103,7 @@ const config = {
     '@typescript-eslint/require-array-sort-compare': 'warn',
     // yes: with types, this is actually useful and correct
     '@typescript-eslint/return-await': 'error',
+    '@typescript-eslint/switch-exhaustiveness-check': 'error',
     '@typescript-eslint/unified-signatures': 'warn', // can be a bit wrong
     'array-callback-return': 'off',
     'block-scoped-var': 'off',