[WIP] Add watch filtering by package-id label (obsolete)

[karlkfi]

go/config-sync-watch-filter

Dependencies:

• Add event handler to Applier/Destroyer #1199
• Fix declared.Resources to be consistently ordered  #1204
• Use field managers for all K8s API calls #1241
• Rename declared.RootReconciler to RootScope #1244

TODO:

• Extract SyncStatusUpdater changes
• Extract conflict handler changes
• Finalize design approval (some open questions about label naming)

[google-oss-prow]

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[karlkfi]

This PR is replaced by #1301, which has less tech debt in it. But I'm going to keep this one open and blocked for a bit so I can mine it for refactoring to do after watch filtering merges.