jenkins_jobs: Add an Alma Linux 8 build

Summary:
This build is meant to verify build and unit test on Red Hat 8 compatible
operating systems.

Replace one centos7 build to conserve resources while maintaining
compiler version coverage.

Test Plan: Jenkins: platform: alma8

Reviewers: mbautin, jharveysmith

Reviewed By: jharveysmith

Subscribers: devops

Differential Revision: https://phabricator.dev.yugabyte.com/D12586

jenkins_jobs.yml

@@ -18,10 +18,10 @@ jobs:
   - os: centos7
     compiler: gcc5
     build_type: release
-  - os: centos7
+  - os: alma8
     compiler: gcc9
     build_type: debug    
-  - os: centos7
+  - os: alma8
     compiler: gcc9
     build_type: release
   - os: macos