Remove "L2tpPsk" from the history

[exchange12rocks]

Prerequisites

• [X] Write a descriptive title.

Description of the new feature/enhancement

Cmdlets Add-VpnConnection, Set-VpnConnection have a parameter -L2tpPsk that contains a secret key shared between the server and the client. I suppose this is a sensitive information and its worth to filter out commands that have this parameter with a clear-text value.

Proposed technical implementation details (optional)

Add "L2tpPsk" into the list https://github.com/PowerShell/PSReadLine/blob/master/PSReadLine/History.cs#L117