Reworked feature flag usage for Hybrid search feature

[martin-gaievski]

Description

Reworked feature flag to a plugin setting. Previous approach is failing with below error when feature is set in opensearch.yml, which supposed to be the main way of enabling hybrid search for customers:

org.opensearch.common.settings.SettingsException: unknown setting [neural_search_hybrid_search_enabled] please check that any required plugins are installed, or check the breaking changes documentation for removed settings
        at org.opensearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:606) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:547) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:517) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.common.settings.AbstractScopedSettings.validate(AbstractScopedSettings.java:487) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.common.settings.SettingsModule.<init>(SettingsModule.java:179) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.node.Node.<init>(Node.java:555) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.node.Node.<init>(Node.java:388) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.Bootstrap$5.<init>(Bootstrap.java:242) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.Bootstrap.setup(Bootstrap.java:242) ~[opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.Bootstrap.init(Bootstrap.java:404) [opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.OpenSearch.init(OpenSearch.java:180) [opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.OpenSearch.execute(OpenSearch.java:171) [opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:104) [opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.cli.Command.mainWithoutErrorHandling(Command.java:138) [opensearch-cli-3.0.0.jar:3.0.0]
        at org.opensearch.cli.Command.main(Command.java:101) [opensearch-cli-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.OpenSearch.main(OpenSearch.java:137) [opensearch-3.0.0.jar:3.0.0]
        at org.opensearch.bootstrap.OpenSearch.main(OpenSearch.java:103) [opensearch-3.0.0.jar:3.0.0]

Added more logging statements for easier debugging.

Issues Resolved

#123

Check List

• All tests pass
• Commits are signed as per the DCO using --signoff

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.

[martin-gaievski]

we need this to have hybrid search always enabled in testing, otherwise we need to set flag explicitly every time

[martin-gaievski]

adding toString to have nicer info in the log, same for all other similar toString annotations

[codecov]

Codecov Report

Merging #246 (dc1dd60) into main (b9c86a8) will increase coverage by 0.05%.
The diff coverage is 93.33%.

@@             Coverage Diff              @@
##               main     #246      +/-   ##
============================================
+ Coverage     86.23%   86.29%   +0.05%     
- Complexity      337      340       +3     
============================================
  Files            28       29       +1     
  Lines           981      992      +11     
  Branches        153      153              
============================================
+ Hits            846      856      +10     
- Misses           69       70       +1     
  Partials         66       66              

Files Changed	Coverage Δ
...ation/ArithmeticMeanScoreCombinationTechnique.java	89.47% <ø> (ø)
...nation/GeometricMeanScoreCombinationTechnique.java	94.11% <ø> (ø)
...ination/HarmonicMeanScoreCombinationTechnique.java	94.11% <ø> (ø)
...r/normalization/L2ScoreNormalizationTechnique.java	83.33% <ø> (ø)
...rmalization/MinMaxScoreNormalizationTechnique.java	84.61% <ø> (ø)
...g/opensearch/neuralsearch/plugin/NeuralSearch.java	77.77% <80.00%> (-3.48%)	⬇️
...neuralsearch/processor/NormalizationProcessor.java	83.87% <100.00%> (+0.53%)	⬆️
...arch/processor/NormalizationProcessorWorkflow.java	88.00% <100.00%> (+3.00%)	⬆️
...ocessor/factory/NormalizationProcessorFactory.java	100.00% <100.00%> (ø)
...ch/neuralsearch/settings/NeuralSearchSettings.java	100.00% <100.00%> (ø)

[opensearch-trigger-bot]

The backport to 2.x failed:

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

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-246-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 5819df61c6ce7d155463f8fcc0ffb4fd4ac3080d
# Push it to GitHub
git push --set-upstream origin backport/backport-246-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-246-to-2.x.