Added support for node 16, formatting and linting (validator-ajv6) (r…

…jsf-team#2932)

* Added support for node 16 and linting
- Regenerated the `package-lock.json` file with node-16
- Added the `cs-check`, `cs-format` and `lint` scripts along with `lint-staged` to the `package.json` file

* - Ran `cs-format` on the `validator-ajv6` source to fix build

* - Switched the `no-unused-vars` rule to `@typescript-eslint/no-unused-vars` in `.eslintrc`

packages/validator-ajv6/.eslintrc

@@ -5,7 +5,7 @@
     "linebreak-style": [2, "unix"],
     "semi": [2, "always"],
     "comma-dangle": [0],
-    "no-unused-vars": [2, {
+    "@typescript-eslint/no-unused-vars": [2, {
       "vars": "all",
       "args": "none",
       "ignoreRestSiblings": true