Add support for symbol packages (.snupkg) to NuGet package registry

Context

You can use the GitLab Package Registry to publish, download and manage your NuGet packages. You can use symbol packages (.snupkg) to distribute these symbols and improve the debugging experience of your NuGet packages.

Problem to solve

The problem is that the GitLab Package Registry does not support symbol packages. This makes it difficult to debug your dependencies.

Proposal

Add support for NuGet symbol packages to the NuGet package registry by implementing the symbol package publish resource (https://docs.microsoft.com/en-us/nuget/api/symbol-package-publish-resource).

Metrics

• Create new snowplow events to measure how often NuGet symbol packages are being published and installed. This will help GitLab to better understand the priority and severity of future feature ideas.