[Docs] Add debug string information

[dhmlau]

Originated from: #4844

In LB3 docs, there's Running and debugging apps page. A similar version for LB4 would be useful.

Acceptance Criteria

• Add Running and debugging apps
• Add setting debug strings as a child page.
  • Note: The connector ones would be the same. For others, not every debug strings would be the same. e.g. strong-remoting

[agnes512]

Closing as done