Index Level Encryption plugin

[asonje]

Description

This pull request adds index level encryption features to OpenSearch based on the issue #3469. Each OpenSearch index is individually encrypted based on user provided encryption keys. A new cryptofs store type index.store.type is introduced which instantiates a CryptoDirectory that encrypts and decrypts files as they are written and read respectively

Related Issues

Resolves #3469

Check List

• [x] New functionality includes testing.
  • [x] All tests pass
• [x] New functionality has been documented.
  • [x] New functionality has javadoc added
• [ ] Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• [x] Commits are signed per the DCO using --signoff
• [x] 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.