Bump BWC Version to 2.18 and Fix Bugs

[kaituo]

Description

This PR includes the following updates and bug fixes:

• Bump BWC Version to 2.18: Updated BWC version to 2.18 since the 2.17 branch has been cut.
• Fix Confidence Value Exceeding 1 in RCF: Addressed a bug in RCF where the confidence value could exceed 1. Implemented a check to cap the confidence value at 1, preventing invalid confidence scores.
• Correct Parameter Assignment in GetAnomalyDetectorTransportAction: Fixed an issue where parameter assignments within a method did not affect external variables due to Java's pass-by-value nature.
• Fixed a bug in ResultProcessor where we were supposed to check whether the number of sent messages equals the number of received messages before starting imputation. However, the sent message count was mistakenly based on the number of pages rather than the actual number of messages.
• Fixed a bug where we mistakenly used the total reserved memory bytes as the memory size per entity in PriorityCache.

Testing done:

• added test cases for the buggy scenarios
• manual e2e testing

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Attention: Patch coverage is 52.94118% with 8 lines in your changes missing coverage. Please review.

Project coverage is 77.52%. Comparing base (3f0fc8c) to head (f6d41a0).
Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
...ensearch/timeseries/transport/ResultProcessor.java	12.50%	7 Missing ⚠️
...d/transport/GetAnomalyDetectorTransportAction.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1311      +/-   ##
============================================
+ Coverage     71.83%   77.52%   +5.69%     
- Complexity     4898     5456     +558     
============================================
  Files           518      533      +15     
  Lines         22879    23333     +454     
  Branches       2245     2311      +66     
============================================
+ Hits          16434    18088    +1654     
+ Misses         5410     4184    -1226     
- Partials       1035     1061      +26     

Flag	Coverage Δ
plugin	77.52% <52.94%> (+5.69%)	⬆️

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

Files with missing lines	Coverage Δ
...in/java/org/opensearch/ad/model/AnomalyResult.java	80.28% <100.00%> (-5.08%)	⬇️
.../org/opensearch/forecast/model/ForecastResult.java	74.74% <100.00%> (+0.26%)	⬆️
...g/opensearch/timeseries/caching/PriorityCache.java	69.54% <100.00%> (+0.39%)	⬆️
...series/transport/BaseGetConfigTransportAction.java	86.26% <100.00%> (+10.43%)	⬆️
...d/transport/GetAnomalyDetectorTransportAction.java	86.66% <50.00%> (+6.66%)	⬆️
...ensearch/timeseries/transport/ResultProcessor.java	75.27% <12.50%> (-1.27%)	⬇️

... and 104 files with indirect coverage changes

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/anomaly-detection/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/anomaly-detection/backport-2.x
# Create a new branch
git switch --create backport/backport-1311-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dbf8785e0718c5e6304729818e05bef64f30987c
# Push it to GitHub
git push --set-upstream origin backport/backport-1311-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/anomaly-detection/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-1311-to-2.x.

[opensearch-trigger-bot]

The backport to 2.17 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/anomaly-detection/backport-2.17 2.17
# Navigate to the new working tree
pushd ../.worktrees/anomaly-detection/backport-2.17
# Create a new branch
git switch --create backport/backport-1311-to-2.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dbf8785e0718c5e6304729818e05bef64f30987c
# Push it to GitHub
git push --set-upstream origin backport/backport-1311-to-2.17
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/anomaly-detection/backport-2.17

Then, create a pull request where the base branch is 2.17 and the compare/head branch is backport/backport-1311-to-2.17.