There should be a way to filter out resources from the final output

[sudohikumar]

The way cue handles exports using -e flag to just give output of specific element, cuestomize should also provide a way to filter out resources from the final output.

Use case

Suppose we have 1 resource that needs to be created beforehand as part of bootstrap. Then we can apply other resources on the cluster.
outputs dumps all the resources in 1 single file by default.
Currently, the way to do using cuestomize are the following

• yq split and search and write our own custom logic for that filtering
• slice all the resources in a folder and again write logic to filter out specific resources
• Have multiple modules exported separately based on the usecase. (I think this adds additional files but cleaner than above 2).

Suppose we have main.cue as follows

...
outputs: {
	cm: #ConfigMap
	deployment: #Deployment 
         ....
}
...

I can simply do this via vanilla cue cli

cue export -e outputs.cm --out yaml
cue export -e outputs.deployment--out yaml

Similar thing is not possible currently here.

Proposals

I propose 2 types of solutions. Both has pros and cons. But it makes filtering easier.

1. Output multiple outputs as keys than can be used to filter out on client side.
   Example:

outputs: {
	controllerResources: {
		cm: #ConfigMap
		deployment: #Deployment 
	}
	baseResources: {
		sa: #SA
		role: #Role
	}
}

This can be further refined if accepted.
2. Similar to includes feature, we also have filter spec than can filter out fields to give final output.
Example:

apiVersion: cuestomize.dev/v1alpha1
kind: Cuestomization
...
filter:
  - group: apps
    version: v1
    kind: Deployment
    name: manager
    namespace: default

This will only give deployment spec with that filter match. This will be client side filtering.