Add toBuilder() method in EngineConfig

[RajatGupta02]

Description

Adding a toBuilder() method for easy modification of specific fields while preserving all other configs.

Motivation

For our opensearch storage encryption plugin, while implementing translog encryption, in our CryptoEngineFactory we needed to create an EngineConfig identical to the original except for the translogFactory (to enable encrypted translogs).

This would mean copying all fields like below, and we would miss the configs if the original configs changed in Builder :

// Must manually copy 25+ fields to change just one field
EngineConfig cryptoConfig = new EngineConfig.Builder()
    .shardId(config.getShardId())
    .threadPool(config.getThreadPool())
    .indexSettings(config.getIndexSettings())
    .warmer(config.getWarmer())
    .store(config.getStore())
    .mergePolicy(config.getMergePolicy())
    .analyzer(config.getAnalyzer())
    .similarity(config.getSimilarity())
    .codecService(getCodecService(config))
    .eventListener(config.getEventListener())
    // ... 15+ more manual field copies
    .translogFactory(cryptoTranslogFactory)  // The only field we actually want to change
    .build();

Hence, with this PR, it enables selective modification of specific fields while preserving others.

Related Issues

Resolves

• Add translog encryption opensearch-storage-encryption#39 (comment)

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 522d865: FAILURE

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[github-actions]

❌ Gradle check result for ce9558c: FAILURE

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[cwperks]

Thank you @RajatGupta02 ! The changes look good to me. For any other maintainer reviewing this PR, you can see the usage here: https://github.com/opensearch-project/opensearch-storage-encryption/pull/39/files#diff-e1145e4d7e594b9d06cdc9d1a8da84d0756b05bbab95c57174ecfa82ada15facR47-R52

The responsibility for ensuring that the builder has all necessary values would fall on the EngineConfig constructor that accepts the builder so I think the changes in here are reasonable.

@andrross @mch2 wdyt?

[github-actions]

❌ Gradle check result for 707c7cf: FAILURE

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[kumargu]

@RajatGupta02 i think we should also point out the problem we were facing in the encryption plugin which motivated us to make this change.

[github-actions]

❌ Gradle check result for 707c7cf: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for 6f58967: SUCCESS

[codecov]

Codecov Report

❌ Patch coverage is 3.22581% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.97%. Comparing base (292407b) to head (6f58967).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...java/org/opensearch/index/engine/EngineConfig.java	0.00%	30 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19054      +/-   ##
============================================
- Coverage     73.02%   72.97%   -0.05%     
+ Complexity    69548    69478      -70     
============================================
  Files          5647     5647              
  Lines        319106   319136      +30     
  Branches      46163    46163              
============================================
- Hits         233034   232900     -134     
- Misses        67232    67423     +191     
+ Partials      18840    18813      -27     

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