frontend: add eslint rule restrict-template-expressions

So that we do not accidentally pass undefined, null, booleans or
just any type in tempalte literals, see:

    `all these should error ${false} ${undefined} ${[]} ${null}`

This is a eslint rule, so only make weblint will check.

frontends/web/.eslintrc.json

@@ -26,7 +26,16 @@
   "overrides": [
     {
       "files": ["**/*.ts?(x)"],
-      "rules": { }
+      "rules": {
+        "@typescript-eslint/restrict-template-expressions": ["error", {
+          "allowAny": false,
+          "allowBoolean": false,
+          "allowNullish": false
+        }]
+      },
+      "parserOptions": {
+        "project": ["./tsconfig.json"]
+      }
     },
     {
       "files": ["**/*.test.ts?(x)"],