Add scripts to install dotnet on windows and ubuntu

[tevoinea]

Summary of the Pull Request

What is this about?

This PR adds scripts to install dotnet and related tooling on ubuntu and windows.

PR Checklist

• Closes Install dotnet and tools on VMs #2005
• Tests added/passed
• Requires documentation to be updated

Info on Pull Request

What does this include?

These scripts were written with the following goals:

• A small footprint regarding system configuration (environment variables, files in 'standard' locations)
• Ease of use by the agent

I made the tradeoff by setting the DOTNET_ROOT environment variable/adding /etc/dotnet/install_location on linux in order to make it easier to call the dotnet tools from the agent.

The alternative approach is that every time we call the dotnet tools from the agent, we must set the DOTNET_ROOT env var for that process every time.

I'm open to both approaches, the reason I chose the current implementation is because there's no way to indicate on the agent that the env var is required so it's easy to make mistakes.

Validation Steps Performed

How does someone test & validate?

• I spun up a fresh ubuntu docker image and ran the script
• I spun up a fresh Win10 VM and ran the script