Add CI_PROJECT_TOPICS predefined variable

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What does this MR do and why?

Add CI_PROJECT_TOPICS predefined variable

Expose a new CI/CD predefined variable, CI_PROJECT_TOPICS, containing a comma-separated list of the project's topics. This allows pipelines to access project topics directly as an environment variable.

References

Predefined CICD Variables

Screenshots or screen recordings

How to set up and validate locally

1. register a runner to execute a CICD job
2. in the script section of a .gitlab-ci.yml, display environment variable with env command for example

Related issue

this resolves issue #557310 (closed)