chore: release 2.1.0 (#441)

* updated CHANGELOG.md [ci skip]

* updated package.json [ci skip]

* updated samples/package.json

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

Author: release-please[bot]

monitoring/snippets/package.json

@@ -14,7 +14,7 @@
     "test": "mocha --timeout 600000"
   },
   "dependencies": {
-    "@google-cloud/monitoring": "^2.0.0",
+    "@google-cloud/monitoring": "^2.1.0",
     "yargs": "^15.0.0"
   },
   "devDependencies": {