Fix server host resolution when host is configured

[wolfkill]

Fixes #17152

Summary

• resolve the server hostname lazily so an explicit pinot.server.netty.host does not evaluate NetUtils.getHostAddress() or NetUtils.getHostnameOrAddress()
• preserve the existing fallback behavior when the host is not configured
• add focused coverage for configured host, address fallback, and hostname fallback

Testing

• JAVA_HOME=/opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk/Contents/Home ./mvnw -pl pinot-server -am -Dtest=BaseServerStarterTest -Dsurefire.failIfNoSpecifiedTests=false test
• git diff --check

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 64.41%. Comparing base (6bff229) to head (1f764e1).
⚠️ Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
.../pinot/server/starter/helix/BaseServerStarter.java	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18625      +/-   ##
============================================
+ Coverage     64.39%   64.41%   +0.01%     
  Complexity     1137     1137              
============================================
  Files          3336     3337       +1     
  Lines        206096   206070      -26     
  Branches      32145    32128      -17     
============================================
+ Hits         132721   132736      +15     
+ Misses        62714    62700      -14     
+ Partials      10661    10634      -27     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-21	64.41% <83.33%> (+0.01%)	⬆️
temurin	64.41% <83.33%> (+0.01%)	⬆️
unittests	64.41% <83.33%> (+0.01%)	⬆️
unittests1	56.82% <ø> (+0.03%)	⬆️
unittests2	36.95% <83.33%> (-0.01%)	⬇️

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