Add docs for Unity

[adams85]

Description

Adds a guide/reference for Unity.

Trello card

n/a

Notes for QA

A new item has been added to the SDK reference list. It should show up in the starting page and the side bar (when viewing both V1 and V2).

Requirement checklist

• [x] I have validated my changes on a test/local environment.
• [x] I have tested that the code snippets I added work. (Leave unchecked if there are no new code snippets.)
• [x] I have added my changes to the V1 and V2 documentations.
• [ ] I have checked the SNYK/Dependabot reports and applied the suggested changes.
• [ ] (Optional) I have updated outdated packages.