chore: create a CI action to download nargo and add to path

[TomAFrench]

Description

Problem*

Resolves

Summary*

This adds an action which downloads nargo from an artifact and adds it to the path.

Unsure if this will work due to being in an action context. 🤷

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.