Enable basic DRA qualifiers

[seanstory]

Part of https://github.com/elastic/search-team/issues/9111

This gives us the ability to specify a VERSION_QUALIFIER env var for a buildkite pipeline, and have that qualifier be picked up when producing staging artifacts.

After this PR is merged, we will trigger a build on main with VERSION_QUALIFIER=alpha1 to produce a 9.0.0-alpha1 pre-release for internal testing.

Checklists

Pre-Review Checklist

• this PR does NOT contain credentials of any kind, such as API keys or username/passwords (double check config.yml.example)
• this PR has a meaningful title
• this PR links to all relevant github issues that it fixes or partially addresses
• this PR has a thorough description
• Tested the changes locally
• Added a label for each target release version (example: v7.13.2, v7.14.0, v8.0.0)
• Considered corresponding documentation changes

[seanstory]

I've confirmed that the outputs look right:

2025-01-16 15:57:25 CST | Contents of 'dra-artifacts' subdir
-- | --
  | 2025-01-16 15:57:25 CST | ++ ls -lah /opt/buildkite-agent/builds/bk-agent-prod-gcp-1737064481463707835/elastic/connectors/dist/dra-artifacts
  | 2025-01-16 15:57:25 CST | total 1.4G
  | 2025-01-16 15:57:25 CST | drwxrwxrwx 2 buildkite-agent buildkite-agent 4.0K Jan 16 21:57 .
  | 2025-01-16 15:57:25 CST | drwxrwxrwx 5 buildkite-agent buildkite-agent 4.0K Jan 16 21:57 ..
  | 2025-01-16 15:57:25 CST | -rw-rw-r-- 1 buildkite-agent buildkite-agent 434K Jan 16 21:57 connectors-9.0.0-alpha1.zip
  | 2025-01-16 15:57:25 CST | -rw-rw-r-- 1 buildkite-agent buildkite-agent 360M Jan 16 21:56 elastic-connectors-9.0.0-alpha1-docker-image-linux-amd64.tar.gz
  | 2025-01-16 15:57:25 CST | -rw-rw-r-- 1 buildkite-agent buildkite-agent 351M Jan 16 21:56 elastic-connectors-9.0.0-alpha1-docker-image-linux-arm64.tar.gz
  | 2025-01-16 15:57:25 CST | -rw-rw-rw- 1 buildkite-agent buildkite-agent 360M Jan 16 21:56 elastic-connectors-9.0.0-docker-image-linux-amd64.tar.gz
  | 2025-01-16 15:57:25 CST | -rw-rw-rw- 1 buildkite-agent buildkite-agent 351M Jan 16 21:56 elastic-connectors-9.0.0-docker-image-linux-arm64.tar.gz
  | 2025-01-16 15:57:25 CST | ++ echo 'We would now execute:
  | 2025-01-16 15:57:25 CST |  
  | 2025-01-16 15:57:25 CST | docker run --rm   --name release-manager   -e VAULT_ADDR   -e VAULT_ROLE_ID   -e VAULT_SECRET_ID   --mount type=bind,readonly=false,src="/opt/buildkite-agent/builds/bk-agent-prod-gcp-1737064481463707835/elastic/connectors/dist",target="/artifacts"   docker.elastic.co/infra/release-manager:latest   cli collect       --project "connectors"       --branch "seanstory/9111-add-dra-qualifier"       --commit "baf771d572ce655fb7efbf8e7d894c3e52d7e873"       --workflow "staging"       --version "9.0.0"       --qualifier "alpha1"       --artifact-set main
  | 2025-01-16 15:57:25 CST | '

[jedrazb]

let's test on prod!

[github-actions]

💔 Failed to create backport PR(s)

The backport operation could not be completed due to the following error:
There are no branches to backport to. Aborting.

The backport PRs will be merged automatically after passing CI.

To backport manually run:
backport --pr 3119 --autoMerge --autoMergeMethod squash