Build and Upload .NET SDK to NuGet automatically

Problem to solve

Users need to download the .NET SDK to use it to add event tracking and instrument their application. They must go to the GitLab repository where we build it and download it to do this, which is confusing and causes extra steps. Instead, they are used to using Install-Package <package-name> commands.

Desired Outcome

Users of the SDK should be able to always download a specific version of the .NET SDK that has already been built via a Install-Package Gitlab.SDK command

Solution Proposal

Add a pipeline to automatically publish from the main branch of the .NET SDK to Nuget so that users can download it with a Install-Package command. Make sure that correct semantic versioning is built-in.