tracing: Replace Provisioning mocks with actual API calls

What does this MR do and why?

Hooking up client with Provisioning API (spec)

Closes gitlab-org/opstrace/opstrace#2271 (closed)

(Note this feature is FeatureFlagged, Experimental and WIP - no active users yet apart from some internal testers )

Screenshots or screen recordings

N/A

How to set up and validate locally

• RSpec

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.