Refactor train index and create index from template APIs in JNI layer

[junqiu-lei]

Description

Follow up from https://github.com/opensearch-project/k-NN/pull/1784, this PR refactors CreateIndexFromTemplate and TrainIndex APIs within JNI layer.

• Moved faiss lib train related function calls to their respective service classes.
• Cleaned up and removed redundant code in faiss wrapper.

Related Issues

Closes https://github.com/opensearch-project/k-NN/issues/1846

Check List

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

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[jmazanec15]

@junqiu-lei Could you provide context around what changes you are making and why? Itll help for review

[junqiu-lei]

@junqiu-lei Could you provide context around what changes you are making and why? Itll help for review

Sure, updated in PR description.

[jmazanec15]

@junqiu-lei Did ./bin/jni_test pass on your local?

[junqiu-lei]

@junqiu-lei Did ./bin/jni_test pass on your local?

Yes, here is the results:

[==========] 74 tests from 39 test suites ran. (492 ms total)
[  PASSED  ] 74 tests.
(base) junqiu@6c7e67cc15a1 jni % git status
On branch refactor-jni-train
Your branch is up to date with 'junqiu/refactor-jni-train'.