Add toggle-able sidebar button

[LukeBillington]

Proposed changes

Adds a sidebar toggle feature that uses localStorage to keep track of user preferences to display or hide the left navigation bar. This is useful for viewing the API docs and having access to navigation.

Closes #42

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes

Screenshots

] I have updated any relevant documentation ([`README.md`](https://github.com/nginxinc/nginx-hugo-theme/blob/main/README.md) and [`CHANGELOG.md`](https://github.com/nginxinc/nginx-hugo-theme/blob/main/CHANGELOG.md))

[nginx-jack]

I'm seeing some issues with the chevron-right. At my normal resolution (3008*1692 - The middle option of scaling with a 4k monitor) - If I zoom in a few clicks it becomes visible.

[JTorreG]

I'm seeing some issues with the chevron-right. At my normal resolution (3008*1692 - The middle option of scaling with a 4k monitor) - If I zoom in a few clicks it becomes visible.

seeing a similar behavior to the one mentioned by Jack.

Browser: Microsoft Edge, zoom 100%
Resolution tested: 2560x1440

at Zoom 125%