Add channel support via RequiredVersion

[johnstep]

Allow users to pass a channel name, such as '18.03', as the RequiredVersion parameter to Install-Package. The channel name is resolved to the latest version, based on the package source.

Signed-off-by: John Stephens johnstep@docker.com

PS C:\> Install-Package Docker -ProviderName DockerMsftProvider -RequiredVersion 18.03 -Force

Name                           Version          Source           Summary
----                           -------          ------           -------
Docker                         18.03.1-ee-1     DockerDefault    Contains Docker EE for use with Windows Server.

@taylorb-microsoft I bumped the version to 1.0.0.5 since the current release is 1.0.0.4, which I could not find in any of the branches here. However, the code otherwise matched this, the master branch.

[msftclas]

All CLA requirements met.

[carlfischer1]

cc @cwilhit