Add /hold to all PRs by default (through template) (#17139)

Author: easyCZ

.github/pull_request_template.md

@@ -62,3 +62,5 @@ Does this PR require updates to the documentation at www.gitpod.io/docs?
       If enabled this will create the environment on GCE infra
 - [ ] with-integration-tests=all
       Valid options are `all`, `workspace`, `webapp`, `ide`, `jetbrains`, `vscode`, `ssh`
+
+/hold