[Query Resource Isolation] Various Improvements and fixes

[praveenc7]

Summary

1. Add support for custom class implementation using reflections to avoid creating a custom implementation of the entire starter class. This follows the convention we generally use for some class in pinot-minion
2. Removing WorkloadBudgetExceeded Error code since it is no longer used and instead SERVER_RESOURCE_LIMIT_EXCEEDED is generalized to be used instead also WorkloadBudgetExceeded conflicts TOO_MANY_REQUESTS error-code leading to issues on broker testing side
3. Fetch workload budgets on startup - Brokers and servers now fetch their assigned workload budgets from the controller during initialization, ensuring budgets are available immediately after restart
4. Broker debug API - Added /debug/queryWorkloadCost endpoints to brokers (matching existing server APIs) for runtime workload inspection
5. Use IdealState for broker resolution - Controller now uses IdealState instead of ExternalView when propagating workload configs, ensuring offline brokers (e.g., during rolling restart) receive updates
6. canAdmitQuery should check whether enforcement is enabled—similar to how WorkloadResourceAggregator does—instead of relying on costCollection. This ensures correct behavior in scenarios where cost collection is active but enforcement is intentionally disabled for workload analysis or monitoring purposes.
7. Foundational metrics to track basic availability for workload

Testing Done

Unit test and Integ test

[codecov-commenter]

Codecov Report

:x: Patch coverage is 38.92617% with 182 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 63.20%. Comparing base (9a5a5cb) to head (8c492c1). :warning: Report is 57 commits behind head on master.

Files with missing lines	Patch %	Lines
...t/spi/accounting/DefaultWorkloadBudgetManager.java	46.53%	45 Missing and 9 partials :warning:
.../common/utils/config/QueryWorkloadConfigUtils.java	36.98%	35 Missing and 11 partials :warning:
...apache/pinot/common/utils/WorkloadBudgetUtils.java	0.00%	38 Missing :warning:
...ot/core/accounting/WorkloadResourceAggregator.java	0.00%	13 Missing :warning:
...t/spi/accounting/WorkloadBudgetManagerFactory.java	64.51%	6 Missing and 5 partials :warning:
...che/pinot/core/query/logger/ServerQueryLogger.java	0.00%	5 Missing :warning:
.../pinot/core/query/scheduler/WorkloadScheduler.java	25.00%	3 Missing :warning:
...e/pinot/broker/api/resources/PinotBrokerDebug.java	0.00%	2 Missing :warning:
.../helix/BrokerUserDefinedMessageHandlerFactory.java	0.00%	2 Missing :warning:
...ache/pinot/server/api/resources/DebugResource.java	0.00%	2 Missing :warning:
... and 4 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17124      +/-   ##
============================================
+ Coverage     63.17%   63.20%   +0.03%     
- Complexity     1428     1429       +1     
============================================
  Files          3104     3107       +3     
  Lines        183488   183594     +106     
  Branches      28127    28141      +14     
============================================
+ Hits         115911   116049     +138     
+ Misses        58611    58561      -50     
- Partials       8966     8984      +18     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (?)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	?
java-11	63.18% <38.92%> (+0.03%)	:arrow_up:
java-21	63.18% <38.92%> (+0.04%)	:arrow_up:
temurin	63.20% <38.92%> (+0.03%)	:arrow_up:
unittests	63.20% <38.92%> (+0.03%)	:arrow_up:
unittests1	56.17% <28.46%> (-0.01%)	:arrow_down:
unittests2	33.62% <16.10%> (+0.02%)	:arrow_up:

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