Introduce weighted load balancer

[Shaddoll]

What changed?
Introduce a weighted load balancer to matching client

Why?
See the documentation in the PR.
This loadbalancer is better than the previous 2 implementations.

How did you test it?
unit test, and also verified in dev environment

Potential risks

Release notes

Documentation Changes

[codecov]

Codecov Report

Attention: Patch coverage is 90.11628% with 17 lines in your changes missing coverage. Please review.

Project coverage is 73.60%. Comparing base (225c0ea) to head (7c2a13b).
Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
client/matching/weighted_loadbalancer.go	90.90%	5 Missing and 5 partials ⚠️
service/matching/handler/engine.go	0.00%	3 Missing ⚠️
service/matching/tasklist/task_list_manager.go	60.00%	1 Missing and 1 partial ⚠️
client/matching/loadbalancer.go	83.33%	1 Missing ⚠️
client/matching/rr_loadbalancer.go	83.33%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
client/matching/client.go	90.55% <100.00%> (+1.07%)	⬆️
client/matching/multi_loadbalancer.go	100.00% <100.00%> (ø)
client/matching/loadbalancer.go	69.69% <83.33%> (-0.31%)	⬇️
client/matching/rr_loadbalancer.go	94.91% <83.33%> (ø)
service/matching/tasklist/task_list_manager.go	68.53% <60.00%> (-0.18%)	⬇️
service/matching/handler/engine.go	79.69% <0.00%> (-0.21%)	⬇️
client/matching/weighted_loadbalancer.go	90.90% <90.90%> (ø)

... and 42 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 225c0ea...7c2a13b. Read the comment docs.

[taylanisikdemir]

I recommend adding a background ticker to log weights. (need to add start/stop to load balancer interface for this.)
This will help a lot for debugging in prod. Global rate limiter is missing this and we are having hard time debugging edge cases.