Add observability settings page

What does this MR do and why?

Add new "Tracing, Metrics & Logs" section under Settings > Monitor.

Closes Improve observability settings page (gitlab-org/opstrace/opstrace#2777 - closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

• Enable observability_tracing FF
• Go to https://local.gitlab.com:3443/flightjs/Flight/-/settings/operations