[Buildkite] Add step to trigger release distribution pipeline

[mrodm]

What is the problem this PR solves?

Missing trigger step in 7.17 to create docker distribution images with all the packages as in main or 8.* branches.

How does this PR solve the problem?

This PR backports these two PRs #2729 and #3043 adds the same step as in main branch to trigger the pipeline https://buildkite.com/elastic/package-registry-release-package-registry-distribution in charge of creating the docker distribution images.

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

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