Remove parent root from desired_config stored in workspace_agentk_state

Issue: Add a background DB migration to populate the w... (#538360 - closed)

What does this MR do and why?

Backfill workspace_agentk_states for all worksp... (!199102 - merged) added migration logic to backfill workspace_agentk_states table for all the existing workspace. This logic is slightly incorrect. The jsonb which is supposed to be stored inside this table is supposed to have an array and we are saving an object. In other words, root level node is not required in this table. The table below should explain it better.

Bad jsonb doc	Good
{ "desired_config_array": [{}, {}, {}] }	[{}, {}, {}]

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