Changes in kubectl apply --prune to support k8s Inclusive Naming Initiative:
* Deprecated the --prune-whitelist flag.
* Deprecated the PruneWhitelist field on ApplyFlags struct.
* Removed PruneWhitelist field (not used anywhere) from ApplyOptions struct.
* Added --prune-allowlist flag.
* Added PruneAllowlist field on ApplyFlags struct.
* Added unit tests for prune with allowlist
This commit also fixes a bug where the command would fail if you specified
the sameGVK multiple times for --allow-whitelist. Now it only attempts to
prune the unique set of allowed GVKs.
Kubernetes-commit: f7ebf4d8852d4500f24100ca9a4ca665efc1fada