Add workflow for publishing Node Agent as an Azure site extension

[mrickard]

Description

The Node Agent should be installable as an App Service Extension for Azure. In order to do this, we need to add a workflow for publishing an appropriately-formed bundle to NuGet. This requires effort in two areas:

1. Adding the necessary structure for the site extension to the agent codebase
2. Creating the Github Actions workflow to publish that bundle to NuGet (this issue)

Azure supports site extensions for Windows only, and the tools required to structure the extension appropriately are Windows-only. The workflow we create should use a Windows runner, and install the appropriate .NET tooling to create the extension. We can use the Java Agent's site extension approach as a reference for determining how to build the properly structured bundle.

The GitHub Actions workflow for Node will

• install the necessary .NET/NuGet tooling to build the site extension bundle
• build the site extension to include the latest New Relic Node agent
• publish to NuGet with a version matching that of the agent

Acceptance Criteria

As an Azure user, I expect to be able to install the Node agent as an App Service Extension.

Design Consideration/Limitations

Azure site extensions support only Windows.
Site extensions run their install script when the application they're part of restarts, so we want the install script to take as little time as possible to complete.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-300162