Add Support to tag a minion as Drained

[krishna-st]

Implements a drain mode for Pinot Minion instances, allowing operators to gracefully scale down minions by preventing new task assignments while allowing existing tasks to complete.

• Extended PUT /instances/{instanceName}/state to support DRAIN state for minion instances
• Draining changes minion tag from minion_untagged → minion_drained, preventing Helix from assigning new tasks
• Leverages Helix's native tag-based task assignment mechanism (.setInstanceGroupTag())

[codecov-commenter]

Codecov Report

:x: Patch coverage is 70.45455% with 13 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 63.28%. Comparing base (82b7d2a) to head (efe2d0f). :warning: Report is 2 commits behind head on master. :white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ntroller/helix/core/PinotHelixResourceManager.java	66.66%	5 Missing and 7 partials :warning:
...er/api/resources/PinotInstanceRestletResource.java	85.71%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17375      +/-   ##
============================================
+ Coverage     63.25%   63.28%   +0.02%     
+ Complexity     1475     1474       -1     
============================================
  Files          3162     3162              
  Lines        188668   188711      +43     
  Branches      28869    28881      +12     
============================================
+ Hits         119348   119427      +79     
+ Misses        60074    60026      -48     
- Partials       9246     9258      +12     

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-11	63.24% <70.45%> (+0.01%)	:arrow_up:
java-21	63.25% <70.45%> (+0.02%)	:arrow_up:
temurin	63.28% <70.45%> (+0.02%)	:arrow_up:
unittests	63.28% <70.45%> (+0.02%)	:arrow_up:
unittests1	55.59% <ø> (-0.01%)	:arrow_down:
unittests2	34.03% <70.45%> (+0.03%)	:arrow_up:

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