📖CAEP: Cluster Resource Set

[sedefsavas]

What this PR does / why we need it:
This PR adds CAEP for implementing Cluster Resource Set that was discussed in Design Doc.

Moving here for getting feedback from a broader audience.

[sedefsavas]

/cc @vincepri @timothysc @fabriziopandini
/kind proposal

I am starting a lazy consensus period ending on May 19th.

[vincepri]

/milestone v0.3.x

[fabriziopandini]

I'm +1 to see this proposal implemented with the namespace restrictions for ClusterResourceSet & the ClusterResourceSetStatus as a separate CRD. This will help to get clusterctl move to manage the new resources..
I have left two suggestions WRT to the ClusterResourceSetStatus but they are optional and can be considered implementation details

[fabriziopandini]

I think this can be simplified by having a simple map of resources; this will also address cases when the same secret/configMap is part of more than one ResourceSet

[sedefsavas]

I think this may cause racing condition if two ClusterResourceSets have same resource and they need to change this from different controller threads. Wdyt?

[fabriziopandini]

I think that i two resource set have the same resource, the resource should be applied only once. In fact, this structure helps to implement this behavior

[vincepri]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sedefsavas, vincepri

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[detiber]

/lgtm