Allow cross-shard dependency check

[stefanprodan]

Use the APIReader client to bypass the controller runtime cache when checking for dependencies. This allows a Kustomization to depend on other Kustomizations managed by different controller shards.

Fix: #1175

[darkowlzz]

Manually tested, inspected and verified that before this change, the client failed to get the object from the cache, and doing a live lookup using the API reader fixes that.

In brief, the controller-runtime client determines that Kustomization is configured to be in the cached and must be present in the cache, refer https://github.com/kubernetes-sigs/controller-runtime/blob/v0.19.0/pkg/client/client.go#L335-L342. But due to the sharding configuration, the cache doesn't contain any of the Kustomizations that don't match with the sharding label selector. This results in an object not found error. As is evident from the code, live lookup is only performed for resources that are configured to not be cached.

LGTM! Thanks for the fix.