Adding xPfxImport DSC Resource

[briantist]

Adds the xPfxImport resource, see PowerShell/DscResources#58

[olljanat]

Very nice feature and works fine at least on my lab :)

Hopefully it will be merged to master on some day.

[briantist]

Thanks @olljanat , I hope so too!

[mgreenegit]

This is very useful. It has been a common ask to be able to handle publicly trusted certs. Great set of tests. I haven't validated it in a lab environment but I see someone has already, so I think we are good to go.

[briantist]

@KarolKaczmarek / @mgreenegit great news, glad to see it merged. Do you guys have a set schedule or roadmap for the changes in dev to make it into master? Thanks!

[KarolKaczmarek]

We tend to merge into master and release to PS gallery every few weeks, the next release is planned in about 3 weeks. Until then, feel free to use feed with our development builds: https://github.com/powershell/dscresources/#development-builds

[KarolKaczmarek]

Also, thanks a lot for contributing @briantist and sorry it took so long to review and merge this PR!

[briantist]

Thank you @KarolKaczmarek ; glad to help. I hope to contribute more in the future.