Decouple release/ Manifests into Separate Files

[askmeegs]

Reason - make the release manifests more modular for kustomize / trainings.

Mirror the structure of kubernetes-manifests/*.yaml and update the hack/ release scripts to not concatenate all the YAML resources together.

[bourgeoisor]

Started working on this here: #716

Note that this might be a tough change, since a lot of external content relies on being able to do kubectl apply -f ./release/kubernetes-manifests.yaml (the one-file manifest)

[NimJay]

Providing an update to cool it down from our "Out of SLO" list:
This project is still on pause because we still need to think about how we'll deal with the impact this will have on tutorials/docs using Online Boutique (i.e., running kubectl apply -f ./release/kubernetes-manifests.yaml).
We also need to think about its impact on the upcoming (2022 Q2) Kustomize integration.

[xtineskim]

Cool down for OSLO again! I believe @NimJay made some progress on this

[NimJay]

We can close this GitHub issue now since:

• /kustomize/base/ now contains a decoupled version of /release/kubernetes-manifests.yaml
• the scripts inside /hack/ now generate the /kustomize/base/ YAML files (when we create a new release of Online Boutique)

We have not deleted /release/kubernetes-manifests.yaml yet since it's used by a lot of tutorials and demos.
We need to first update those tutorials and demos before deleting /release/kubernetes-manifests.yaml.