Remove support for Java 8

[dblock]

Is your feature request related to a problem?

Because Apache Lucene 9 requires JDK 11 or newer, remove support for Java 8.

Do you have any additional context?

In #64 we ensured OpenSearch 1.x support for Java 8, 11, and 17, shipping with bundled JDK17. For 2.0 remove support for Java 8

OpenSearch

• Modernize and consolidate JDKs usage across all stages of the build. Update JDK-14 requirement, switch to JDK-17 instead OpenSearch#1368
• Support Gradle 7 OpenSearch#1609
• Remove support for Java 8 OpenSearch#1689

Plugins

• Upgrade to Gradle 7 #107
• Remove support for JDK 8 alerting#325
• Remove support for JDK 8 anomaly-detection#398
• Remove support for JDK 8 asynchronous-search#100
• Remove support for JDK 8 common-utils#124
• Remove support for JDK 8 reporting#301
• Remove support for JDK 8 index-management#289
• Remove support for JDK 8 job-scheduler#136
• Remove support for JDK 8 k-NN#311
• Remove support for JDK 8 performance-analyzer#154
• Remove support for JDK 8 performance-analyzer-rca#141
• Remove support for JDK 8 security#1669
• Remove support for JDK 8 sql#466
• Remove support for JDK 8 observability#547
• Remove support for JDK 8 cross-cluster-replication#330

[dblock]

@reta @dvenable @martin-gaievski is opensearch-project/k-NN#220 (comment) the only reason why we're dropping JDK 8 in 2.0? We should provide a strong(er) justification above.

[reta]

@dblock I think the only reason would be [1], since Apache Lucene 9.0 is setting JDK-11 baseline.

[1] opensearch-project/OpenSearch#1109

[dblock]

@dblock I think the only reason would be [1], since Apache Lucene 9.0 is setting JDK-11 baseline.

[1] opensearch-project/OpenSearch#1109

Right on. Thanks. I updated the issue.

[dblock]

I've started drafting a blog post, please contribute!

opensearch-project/project-website#670