Make Tracing UI a EE Ultimate feature

What does this MR do and why?

Restrict Tracing to EE Ultimate users. Followed https://docs.gitlab.com/ee/development/ee_features.html

Closes gitlab-org/opstrace/opstrace#2276 (closed)

Screenshots or screen recordings

• CE

• Ultimate

How to set up and validate locally

• Run with/without FOSS_ONLY=1 and check that Tracing is available/unavailable (https://local.gitlab.com:3443/flightjs/Flight/-/tracing)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.