CI artifact report keyword for cluster applications

What does this MR do?

First part of #35672 (closed)

Add CI keyword for a cluster applications artifact report

The idea is that we will allow CI/CD managed applications to report back the list of installed applications back to GitLab CI. The format supported is Helm v2 list with json output format. Parsing of the artifact and changing Managed-Cluster-Applications.gitlab-ci.yml to use the keyword will be done in subsequent MRs.

Related issue: #35672 (closed)

This is GL specific and used only by internal GitLab code so no updates to https://docs.gitlab.com/ee/ci/yaml/ is required

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.