Enhance template tests and add dotnet cli APIs for new command

Description

This PR enhances the code in Fake.DotNet.Cli.IntegrationTests project which test the FAKE template. The enhancement include adding a new APIs to Fake.DotNet.Cli to support dotnet new command. The APIs are as follows:

`dotnet new`

A usage example is as follows:

DotNet.newFromTemplate "web" id

The command available options can be found at this documentation page. The supported options are: --dry-run --force --language --name --no-update-check --output

`dotnet new --install`

A usage example is as follows:

DotNet.installTemplate "fake-template" id

The command available options can be found at this documentation page. The supported options are: nuget-source

`dotnet new --uninstall`

A usage example is as follows:

DotNet.uninstallTemplate "fake-template"

The uninstall command has no options.

Not sure if the naming of the APIs is descriptive and is good. If anyone has better ideas or suggestions. Please comment and review the changes.

Thanks

TODO

Feel free to open the PR and ask for help

[x] New (API-)documentation for new features exist (Note: API-docs are enough, additional docs are in help/markdown)
[x] unit or integration test exists (or short reasoning why it doesn't make sense)

Note: Consider using the CreateProcess API which can be tested more easily, see https://github.com/fsharp/FAKE/pull/2131/files#diff-4fb4a77e110fbbe8210205dfe022389b for an example (the changes in the DotNet.Testing.NUnit module)
[x] boy scout rule: "leave the code behind in a better state than you found it" (fix warnings, obsolete members or code-style in the places you worked in)
[ ] Fake 5 API guideline is honored

fsprojects / FAKE