Replace centos:8 with almalinux:8 since centos docker images are deprecated

[cwperks]

Description

This PR changes all instances of centos:8 to almalinux:8 given that the CentOS docker images are marked as deprecated: https://hub.docker.com/_/centos

This resolves an issue seen when incrementing the 2.19 branch to 2.19.4: #18835

> Task :distribution:docker:buildDockerImage FAILED
Exec output and error:
| Output for docker:Error response from daemon: Get "https://registry-1.docker.io/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
Attempt 10/10 to pull Docker base image centos:8 failed

> Task :distribution:archives:buildNoJdkDarwinArm64Tar
> Task :distribution:packages:buildNoJdkArm64Rpm

[Incubating] Problems report is available at: file:///home/runner/work/OpenSearch/OpenSearch/build/reports/problems/problems-report.html

FAILURE: Build failed with an exception.

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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.

[github-actions]

❌ Gradle check result for 2c1a469: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for ceacc7e: SUCCESS

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.87%. Comparing base (816e711) to head (ceacc7e).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/main/java/org/opensearch/gradle/DockerBase.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #19154      +/-   ##
============================================
+ Coverage     72.86%   72.87%   +0.01%     
+ Complexity    69448    69437      -11     
============================================
  Files          5648     5648              
  Lines        319329   319329              
  Branches      46194    46194              
============================================
+ Hits         232684   232723      +39     
+ Misses        67816    67750      -66     
- Partials      18829    18856      +27     

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[prudhvigodithi]

Adding @peterzhuamazon

[prudhvigodithi]

Coming from this issue opensearch-project/opensearch-build#4379, looks like still we are using a combination of al2 and almalinux8 https://github.com/opensearch-project/opensearch-build/blob/main/manifests/3.2.0/opensearch-3.2.0.yml#L10-L21.

I'm ok with this PR to use almalinux8.

[peterzhuamazon]

Not many strong opinion on this because build side is not using this image anyway.

But seems good as alma8 is a direct replacement of centos8 for this purpose.

Thanks.

[opensearch-trigger-bot]

The backport to 2.19 failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/OpenSearch/backport-2.19 2.19
# Navigate to the new working tree
pushd ../.worktrees/OpenSearch/backport-2.19
# Create a new branch
git switch --create backport/backport-19154-to-2.19
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 eae84a49d9052eb09e18c167f3aeaf1cf4467941
# Push it to GitHub
git push --set-upstream origin backport/backport-19154-to-2.19
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/OpenSearch/backport-2.19

Then, create a pull request where the base branch is 2.19 and the compare/head branch is backport/backport-19154-to-2.19.