[Deprecation] Properly deprecate Ubuntu2004 as CI build image/Supported OS and switch to Ubuntu2404

[peterzhuamazon]

Similar to #4379, Ubuntu2004 is about to reach its standard security support and maintenance on 2025/04/02: https://ubuntu.com/about/release-cycle.

Three CI images (NOT release images) related to Ubuntu2004 would needs to be deprecated and replaced:

docker/ci/dockerfiles/current/test.ubuntu2004.systemd-base.x64.arm64.ppc64le.dockerfile
docker/ci/dockerfiles/current/build.ubuntu2004.opensearch.x64.arm64.ppc64le.dockerfile
docker/ci/dockerfiles/current/docker-builder.ubuntu2004.x64.dockerfile

We do not expect any breaking changes happening as all the bundles are built on AL2 before moving to build.ubuntu2004.opensearch.x64.arm64.ppc64le.dockerfile for DEB generation.

The docker builder image might take a bit effort as docker version has changed and dockerx would replace the standard docker build, but we may able to keep the original behavior for the time being.

Similar announcement: https://github.com/opensearch-project/opensearch-build/blob/main/release-notes/opensearch-release-notes-2.12.0.md#deprecation-notice

Thanks.

[peterzhuamazon]

Plan to keep 2.19.0 with Ubuntu2004 and possible of moving Ubuntu2404 to 3.0.0.

cc: @getsaurabh02 @jhmcintyre

Thanks.

[peterzhuamazon]

PRs:

• Replace Ubuntu 20.04 with Ubuntu 24.04 as it will be deprecated soon documentation-website#9165

[peterzhuamazon]

The deprecation notice will be sent out alongside 2.19.0 release.