Use the appropriate port when redirecting node-agents to leader

[xvello]

What does this PR do?

The query port is not available in the request.URL object, making the current redirection code send node-agents on the 443 port.

Assume all DCAs listen on the same port and use the cluster_agent.cmd_port option during redirection.

[codecov-io]

Codecov Report

Merging #2892 into master will decrease coverage by 0.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #2892      +/-   ##
==========================================
- Coverage   57.37%   57.36%   -0.02%     
==========================================
  Files         393      393              
  Lines       25706    25707       +1     
==========================================
- Hits        14748    14746       -2     
- Misses       9986     9989       +3     
  Partials      972      972

Impacted Files	Coverage Δ
pkg/clusteragent/clusterchecks/handler.go	71.77% <0%> (-0.59%)	⬇️
pkg/clusteragent/clusterchecks/api.go	100% <100%> (ø)	⬆️
pkg/logs/input/listener/tailer.go	86% <0%> (-4%)	⬇️
pkg/forwarder/domain_forwarder.go	91.33% <0%> (-1.58%)	⬇️
pkg/secrets/secrets.go	65.04% <0%> (+1.94%)	⬆️

[CharlyF]

good catch