Conditions page improvement

[DrMegavolt]

https://www.express-gateway.io/docs/policies/customization/conditions

• Add simple example before advanced
• Provide navigation links (contents) to jump to conditions
• add copy button to make it possible to copy paste example without breaking indentation

cc @minotaurrr

[DrMegavolt]

incorrect doc for pathMatch

[jcfrane]

incorrect doc for not. Spent 3 hours only to know that the second condition doesn't need indention.