[Release 3.0] Prepare for 3.0 release on Helm Charts

[peterzhuamazon]

With 3.0 is on track to be released early 2025, we will setup plans to make helm charts compatible with 3.0.

Issues:

• [META] OpenSearch 3.0 Core Release Tracker  OpenSearch#16935
• [RELEASE] Release version 3.0.0 opensearch-build#3747
• [PROPOSAL] OpenSearch Release Schedule for Year 2025 .github#252

Steps:

• Create 2.x branch based on main
• Deprecate 1.x
• Upgrade main to 3.x

Thanks.

[peterzhuamazon]

We will create 2.x branch and make main 3.0.0 once GA it out.

Thanks.