error message for `unstake` is not user friendly

Currently during stake pool unlock, we show this error

it should be more like:

sp-unlock not allowed until all active allocations are cancelled by respective owners. So that users know the reason for the error.

Look for the error message shown during stake pool unlock in the CLI codebase, likely in a command handling file like `cmd/unstake.go` or similar. Find where the current generic error is generated and update it to the more descriptive text provided. Test the change by running the unstake command in a scenario with active allocations to verify the new message appears.

Scritto dal modello di indicizzazione a partire dal testo della issue.