Add pagent support

[phobot]

Hello Devs,

It would be nice to have pagent support in the ssh client (I'm aware of the windows ssh agent developed in this project).
My feeling is that this has wide adoption and integration with multiple 3rd party clients. In my case all keys are loaded when keepass database is unlocked and keepass emulates the pagent.
Thus avoiding the pitfall of having passwordless ssh keys but with added convince of not unlocking every key by itself.

Either having the ssh client check the pagent or having the windows ssh agent proxy (mirror) the content of the pagent seem like acceptable solutions.

Thanks for considering,
Have a nice day.

[coocooman3]

FYI, for whatever reason issues for this project are tracked in another github: https://github.com/powershell/Win32-OpenSSH
I have no idea why, but all the work is done in this repo and the issues are managed in that repo. Doesn't make sense, and it's easy to miss the one sentence mentioning it on this project homepage.

[bagajjal]

Please open a new issue at https://github.com/PowerShell/Win32-OpenSSH/issues