[Backport 2.x] bump rcf to 3.0-rc2.1

[opensearch-trigger-bot]

Backport 8227e32 from #519

[codecov-commenter]

Codecov Report

Merging #534 (9474ad8) into 2.x (5b2f2c8) will decrease coverage by 0.17%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                2.x     #534      +/-   ##
============================================
- Coverage     79.17%   79.00%   -0.18%     
+ Complexity     4217     4203      -14     
============================================
  Files           296      296              
  Lines         17681    17681              
  Branches       1877     1877              
============================================
- Hits          13999    13968      -31     
- Misses         2788     2814      +26     
- Partials        894      899       +5     

Flag	Coverage Δ
plugin	79.00% <100.00%> (-0.18%)	⬇️

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

Impacted Files	Coverage Δ
.../main/java/org/opensearch/ad/ml/CheckpointDao.java	69.55% <ø> (-0.65%)	⬇️
.../java/org/opensearch/ad/AnomalyDetectorPlugin.java	96.53% <100.00%> (ø)
...java/org/opensearch/ad/task/ADBatchTaskRunner.java	82.06% <0.00%> (-3.96%)	⬇️
...ava/org/opensearch/ad/task/ADHCBatchTaskCache.java	90.12% <0.00%> (-2.47%)	⬇️
...ain/java/org/opensearch/ad/task/ADTaskManager.java	76.67% <0.00%> (-0.46%)	⬇️
...rch/ad/transport/AnomalyResultTransportAction.java	80.82% <0.00%> (+0.68%)	⬆️
...ansport/handler/AnomalyResultBulkIndexHandler.java	70.96% <0.00%> (+3.22%)	⬆️