chore(kuma-cp): improve test xds client

[jakubdyszkiewicz]

Test XDS client currently was broken, because it was used a long time ago when we were on API V2.
I updated it to API V3. It's helpful in CP benchmarking without spawning thousands of Envoys.

On top of that, it does not present a realistic scenario.
Every DP had 10 inbounds and 10 outbound to every service. It means that with 2000 DPP every service has 2000 endpoints. In the real world, 1 DP has 1-2 inbounds and ~3-5 outbounds (with reachable services). I adjusted the code so you can decide how many inbounds and outbound a single DP has.

Checklist prior to review

• Link to docs PR or issue --
• Link to UI issue or PR --
• Is the issue worked on linked? --
• The PR does not hardcode values that might break projects that depend on kuma (e.g. "kumahq" as a image registry) --
• The PR will work for both Linux and Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Unit Tests --
• E2E Tests --
• Manual Universal Tests --
• Manual Kubernetes Tests --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here?

[lahabana]

Thx!