update docs about multiple controller deployment

[M00nF1sh]

Issue

update docs about multiple controller deployment

See also:

1. ELB Registered Targets go Unhealthy periodically #2178
2. Multiple ALB controllers targeting single work group cause security group collisions #2183

Description

The v2.0.0+ version of AWSLoadBalancerController currently only support one controller deployment(with one or multiple replicas) per cluster.

The AWSLoadBalancerController assumes it's the solo owner of worker node security group rules with elbv2.k8s.aws/targetGroupBinding=shared description, running multiple controller deployment will cause these controllers compete with each other updating worker node security group rules.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[codecov-commenter]

Codecov Report

Merging #2186 (4d86449) into main (b382a94) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #2186   +/-   ##
=======================================
  Coverage   52.29%   52.29%           
=======================================
  Files         132      132           
  Lines        7234     7234           
=======================================
  Hits         3783     3783           
  Misses       3157     3157           
  Partials      294      294           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b382a94...4d86449. Read the comment docs.

[kishorj]

/lgtm