[Tiered caching] Introducing cache plugins and exposing Ehcache as one of the pluggable disk cache option

[sgup432]

Description

Integrating ehcache as a disk cache option which is needed as part of tiered caching. Exposing it as a plugin.
Ehcache Details:

• Disk based cache uses LFU and it is not configurable
• Disk writes are performed asynchronously using separate thread pool.
• Supports cache event listeners.

This change also includes refactoring existing interfaces and moving tieredCache to a module.

Using below settings, anyone can set desired cache:

indices.request.cache.store.name: opensearch_onheap
indices.request.cache.opensearch_onheap.size: 100kb

indices.request.cache.store.name: ehcache_disk
indices.request.cache.ehcache_disk.max_size_in_bytes: 1000

indices.request.cache.store.name: tiered_spillover
indices.request.cache.tiered_spillover.onheap.store.name: opensearch_onheap
indices.request.cache.tiered_spillover.disk.store.name: ehcache_disk
indices.request.cache.opensearch.size: 100kb
indices.request.cache.ehcache_disk.max_size_in_bytes: 1000

Testing

• Added appropriate unit tests.
• We have been POC/performance testing with ehcache. Will be doing another round.

Related Issues

Resolves #11897
and #12296

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• 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.

[sgup432]

@sohami @Bukhtawar

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[codecov]

Codecov Report

Attention: Patch coverage is 82.20339% with 84 lines in your changes are missing coverage. Please review.

Project coverage is 71.39%. Comparing base (7921175) to head (081e269).
Report is 1 commits behind head on main.

Files	Patch %	Lines
.../opensearch/cache/store/disk/EhcacheDiskCache.java	75.00%	38 Missing and 9 partials ⚠️
...search/cache/common/tier/TieredSpilloverCache.java	92.23%	7 Missing and 1 partial ⚠️
.../java/org/opensearch/cache/EhcacheCachePlugin.java	20.00%	8 Missing ⚠️
.../cache/common/tier/TieredSpilloverCachePlugin.java	30.00%	7 Missing ⚠️
...org/opensearch/cache/EhcacheDiskCacheSettings.java	90.90%	2 Missing and 1 partial ⚠️
.../store/settings/OpenSearchOnHeapCacheSettings.java	82.35%	2 Missing and 1 partial ⚠️
.../opensearch/common/cache/service/CacheService.java	88.23%	1 Missing and 1 partial ⚠️
...arch/common/cache/store/OpenSearchOnHeapCache.java	83.33%	2 Missing ⚠️
...n/java/org/opensearch/common/settings/Setting.java	75.00%	1 Missing and 1 partial ⚠️
...ache/common/tier/TieredSpilloverCacheSettings.java	80.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #11874      +/-   ##
============================================
+ Coverage     71.37%   71.39%   +0.01%     
- Complexity    59891    59904      +13     
============================================
  Files          4972     4980       +8     
  Lines        281783   282131     +348     
  Branches      40910    40937      +27     
============================================
+ Hits         201136   201434     +298     
- Misses        63977    64008      +31     
- Partials      16670    16689      +19     

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[peternied]

@sgup432 Great work - thanks for the investment in this space!