Docs: Add debugging guide for Pages

• Start this issue's title with Docs: or Docs feedback:.

Problem to solve

Customer/Support people reports challenges over slack. This issue is to add debugging guide for Pages to make things easier for them.

Further details

1. Include architecture
2. Where to find logs: Railes, Pages, NGINX
3. How to use correlation ID
4. Pages auth flow

Proposal

Who can address the issue

Other links/references