Add notifyOnAttach option

[jborean93]

PR Summary

Adds the new notifyOnAttach option for an attach request. This option will have PSES create a new event with the source identifier PSES.Attached that allows the attached script to wait for the attach event.

Should wait until https://github.com/PowerShell/PowerShellEditorServices/pull/2250 is merged (or rejected).

PR Checklist

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• [x] Summarized changes
• [NA] PR has tests
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