Sidebar V3 Mobile Support

[lamATnginx]

Proposed changes

Closes https://github.com/nginxinc/docs-platform/issues/466 and https://github.com/nginxinc/docs-platform/issues/490

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
• I have updated any relevant documentation (README.md and CHANGELOG.md)

[lamATnginx]

Besides the attached alignment issue, this is ready for review:

[nginx-jack]

This is looking great, and mobile sidebar is a new feature :D.
I'm not sure about the sticky breadcrumb for desktop though? Make sense for mobile, but it consumes limited vertical space on desktop. What do you think?

[lamATnginx]

This is looking great, and mobile sidebar is a new feature :D. I'm not sure about the sticky breadcrumb for desktop though? Make sense for mobile, but it consumes limited vertical space on desktop. What do you think?

Thanks for reviewing! Ahh I see what you mean, I agree on desktop, it is overkill and honestly half-baked where the content goes into a weird void - missing some shadow to indicate more content above. Though I can see some arguments about consistency. I will remove the sticky for all scopes (e.g. mobile, ipad, desktop) for now and in future PR, if enough complaints, we can add it back in for all scopes.

[lamATnginx]

This PR and branch is completely broken due to merged commits not being signed. Dup of #252