Modify a different path for admins on Windows with OpenSSH Server

[pawelszramowski]

Fixes #7107.

I shortly investigated programmatic discovery of authorized keys file path but it doesn't seem easily possible (most importantly, authorizedkeysfile is not shown by ssh -G) so let's leave the choice to the users.

[pawelszramowski]

@microsoft-github-policy-service agree

[bamurtaugh]

Thanks so much for the contribution @pawelszramowski! Left one nit formatting suggestion.

cc @roblourens to ensure this looks good to you too

[pawelszramowski]

@roblourens ping