add DRA version bump pipeline

[ninalee12]

What is the problem this PR solves?

Hi Team,

This PR is the first phase of the version-bump automation rollout as mentioned in #mission-control. It introduces a generalized Buildkite pipeline for service teams in the DRA process. The baseline pipeline includes a block step that waits for each team to unblock before polling for DRA artifacts using a buildkite plugin json-watcher-buildkite-plugin for the polling.

How does this PR solve the problem?

// Explain HOW you solved the problem in your code. It is possible that during PR reviews this changes and then this section should be updated.

How to test this PR locally

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

Related issues

• https://github.com/elastic/observability-robots/issues/3404
• If you haven't already, please provide the Slack channel name for notifications via a comment here or on the issue listed above

[mergify]

This pull request does not have a backport label. Could you fix it @ninalee12? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-./d./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[ebeahan]

LGTM.