Easier quickstart for PipeCD

[khanhtc1202]

What would you like to be added:

We have pipectl quickstart command, but it still requires many things to be prepared before touching pipecd. Say, we need

1. install pipectl
2. having a k8s cluster and kubectl
3. install helm
4. run...

Most of our users may already have (2), so it could be better to remove (1) and (3). I want to serve pre-prepared quickstart manifests, and users can simply run kubectl apply, which could be way easier.

Why is this needed:

[khanhtc1202]

Tasks:

• Make quickstart dir under the main repo containing raw Kubernetes manifests for quickstart (build by helm template command)
• Add CI step update the quickstart manifests on release