Upgrade the version of Elasticsearch used in GDK to 7.15.1

What does this Merge Request do and why?

Related to #1343 (closed)

We are planning on upgrading our production environment to 7.15.1 so we want to use the same version in local development.

CI MR to update Elasticsearch to 7.14.2 (7.15.1 is not published to Dockerhub yet) : gitlab!72651 (merged)

Elastic version 17.15.1 was verified in CI using commit (e81a16fc12a74ab2d3217b30bf9ddc50632ee0e5) with pipeline: https://gitlab.com/gitlab-org/gitlab/-/pipelines/392036368

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.