Expand SSH tables to support Windows

[puffyCid]

Starting with Windows 10 1803, Windows now includes a SSH client (OpenSSH) by default.
This minor PR simply expands the existing ssh_configs and user_ssh_keys tables to support Windows.
Let me know if there are any issues.

[muffins]

lgtm! @puffyCid do you happen to know if we could get the unit/integration tests for these tables working on Windows too? Are they already running? That might make a really nice addition to this diff, or a good follow-up issue for someone to take on.

[theopolis]

Yeah that's a good call out @muffins, we should change the CMake logic such that the integration tests for these tables run on Windows too. https://github.com/osquery/osquery/blob/master/tests/integration/tables/CMakeLists.txt#L125

[puffyCid]

I moved the tables to support Windows tests. But currently it looks like the tests are not implemented to test anything.
Is it even possible to create a specific test for these tables?
Are there dummy user_ssh keys in the Windows VM used to build/test osquery?
Also by default I believe there is no ssh_config for the builtin ssh client for Windows, you have to manually make a config file/directory

[muffins]

@puffyCid ah good call, I'd say we don't need to stress too much about adding in new tests, (if you are feeling up for it though, yeah a good test would be to write out some simple test SSH keys and clean them up after, or do some clever mocking). I mostly wanted to ensure that we had tests hooked up, so if we get tests for the other tables they'll apply to Windows too. I'd say just moving the integration tests to build for all platforms should be sufficient. Thanks!