Use pipe-fittings `utils.PidExists` func in service shutdown code instead of the steampipe version

[pskrbasu]

We should look to use pipe-fittings/v2/utils.PidExists instead of this function in stop_services.go.
Currently, when using the pipe-fittings function, we see some errors with the pids not being found resulting in unsuccessful service shutdowns.

[github-actions]

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