Add rollForward note in README, improve proxy health check in e2e tests and bump version to v5.3.0 (#738)

* docs: add note about latest* rollForward support in global.json

* update health check options for squid proxy in e2e tests

package.json

@@ -1,6 +1,6 @@
 {
   "name": "setup-dotnet",
-  "version": "5.0.1",
+  "version": "5.3.0",
   "private": true,
   "description": "setup dotnet action",
   "main": "dist/setup/index.js",