[Deprecation] Properly deprecate AL2 and switch OS build image to Almalinux8

[peterzhuamazon]

[Deprecation] Properly deprecate AL2 and switch OS build image to Almalinux8

Similar to #4379, we will need to deprecate AL2 and switch to Almalinux8 by 2025/06/30.

It is extended to 2026 for another year: https://aws.amazon.com/amazon-linux-2/faqs/

https://github.com/endoflife-date/endoflife.date/pull/6443/files#diff-1f115483df16fbaab97ea1c43e86394d3d40ab2b7cdc56fad778b57f001779faR38-R39

We already create the image just need to follow up with a few more steps of testing and switch:

• Switch timing (3.2.0): [PROPOSAL] OpenSearch Release Schedule for Year 2025 .github#252
• Deprecate notice
• KNN update gcc similar to this: Bump up GCC version to 12.x or later to support SIMD AVX512 fp16 instructions #5226
• Switch all the OS build image of Jenkins and GitHub checks to Almalinux8 one (2.x and 3.x?)
• Note: [Upgrade] Migrate build repo code from using Python 3.9 to 3.12 version #4994
• 3.0.0 Impact: [PROPOSAL] Release OpenSearch 3.0 .github#250
• 3.0.0 Impact: [Renew Key] Upcoming expiration of our current/old (C5B7 4989 65EF D1C2 924B A9D5 39D3 1987 9310 D3FC) sub public key (expire on 20250512) #4669 as we move to the LF.
• More ......

Thanks.

[krisfreedain]

Catch All Triage - 1, 2, 3