support configuring initial broker tags even when single-tenant mode is enabled

[dang-stripe]

This allows configuring initial broker tags, regardless of cluster isolation mode.

Cluster isolation mode is a rather obscure setting that's not well documented and defaults to true. Currently it controls whether brokers/servers should use DefaultTenant tags or broker_untagged and server_untagged. It seems like it should be removed longer-term, but that has a lot more widespread ramifications.

cc @Jackie-Jiang

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 63.64%. Comparing base (59551e4) to head (3b21b15).
Report is 1587 commits behind head on master.

Files with missing lines	Patch %	Lines
...e/pinot/broker/broker/helix/BaseBrokerStarter.java	12.50%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #14824      +/-   ##
============================================
+ Coverage     61.75%   63.64%   +1.89%     
- Complexity      207     1515    +1308     
============================================
  Files          2436     2707     +271     
  Lines        133233   151207   +17974     
  Branches      20636    23344    +2708     
============================================
+ Hits          82274    96234   +13960     
- Misses        44911    47730    +2819     
- Partials       6048     7243    +1195     

Flag	Coverage Δ
custom-integration1	?
integration	0.00% <ø> (-0.01%)	⬇️
integration1	?
integration2	0.00% <ø> (ø)
java-11	0.00% <ø> (-61.71%)	⬇️
java-21	63.64% <12.50%> (+2.01%)	⬆️
skip-bytebuffers-false	63.63% <12.50%> (+1.88%)	⬆️
skip-bytebuffers-true	56.17% <ø> (+28.44%)	⬆️
temurin	63.64% <12.50%> (+1.89%)	⬆️
unittests	63.64% <12.50%> (+1.89%)	⬆️
unittests1	56.19% <ø> (+9.30%)	⬆️
unittests2	34.04% <12.50%> (+6.31%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.