Update CLI project to drop support for .NET Framework 4.x

[AdmiringWorm]

As part of the history of git release manager, we also provided a full .NET Framework editions.
My suggestion is to drop this support, and instead make use of a standalone .NET Core project instead of the CLI project which do not have any framework dependency, as in the way we provide the project there is no need to have multiple target frameworks and should use what would be easiest to use.