[8.19] Add missing qualifier.sh for DRA staging

[gurevichdmitry]

Summary of your changes

Staging DRA on 8.19 fails in dra-generate.sh because it sources .buildkite/scripts/qualifier.sh, which was never on this branch.

The dra-prep backport (#8301 / #8061) added that source for staging so stack_version can include an alpha/beta qualifier. qualifier.sh itself landed on main/9.x in #2950 and was not part of the 8.19 backport.

This PR adds only that file (same contents as main). The rest of #2950 is not required: 8.19's pipeline already dropped the old VERSION_QUALIFIER conditions, publish.sh is no longer used, and packaging already succeeded without sourcing the file.

Failed job: https://buildkite.com/elastic/cloudbeat/builds/4565#01a07a75-ec9c-4bfe-a151-f76b49e503f1

Screenshot/Data

N/A — CI script fix.

Related Issues

• Failed Buildkite job: https://buildkite.com/elastic/cloudbeat/builds/4565#01a07a75-ec9c-4bfe-a151-f76b49e503f1
• Introduced by: [8.19](backport #8061) Migrate DRA GCS publishing from Release manager to dra-prep-plugin #8301

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary README/documentation (if appropriate)

Test plan

• Confirm CI on this PR is green
• After merge, rerun / wait for the 8.19 Buildkite pipeline and confirm Generate DRA steps (staging) sources qualifier.sh and proceeds past the previous No such file or directory error

Made with Cursor

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