Choco API's: Support for total progress bar and cancellation

If choco downloads and/or installs multiple packages, there should be mechanism to observe total percentage, not only for local file.

`chocolatey\infrastructure.app\nuget\NugetCommon.cs`
`packageDownloader.ProgressAvailable += (sender, e) =>`

this event mechanism observes download progress of one file.

=> Need to have support for multiple files

Also at the moment choco does not provide mechanism for end-user to be able to cancel the download or install operation gracefully - newer API should support it.

`src\chocolatey\infrastructure\commands\Execute.cs`
`var cancelToken = new CancellationTokenSource();`

=> This should be centralized, and provided to end-user of API.

Start by reading chocolatey\infrastructure.app\nuget\NugetCommon.cs around packageDownloader.ProgressAvailable to understand the current single-file progress event. Then inspect src\chocolatey\infrastructure\commands\Execute.cs around the CancellationTokenSource. Done means the API supports total progress across multiple package operations and exposes graceful cancellation to end users.

Written by the indexing model from the issue text.