Add support for MSBuild options to enable RestoreLockedMode

[SIkebe]

Recently NuGet introduced packages.lock.json to enable repeatable package restore and added options to enable locked mode.
https://blog.nuget.org/20181217/Enable-repeatable-package-restores-using-a-lock-file.html

dotnet.exe restore --locked-mode
msbuild.exe /t:restore /p:RestoreLockedMode=true

It'd be great if Cake support those options natively.

[devlead]

@SIkebe agreed, marking as up for grabs 👍
Sidenote, remarks on property should be documented minimal supported MSBuild / .NET CLI version.

• Visual Studio 2017 version 15.9 and above.
• .NET SDK version 2.1.500 and above.

[fseegraeber]

I'd be happy to take a look at this if it's ok.

We're talking about extending MSBuildSettings and MSBuildSettingsExtensions right?

[devlead]

@fseegraeber sure go ahead, I'll remove up-for-grabs / help wanted tags.