Add description metadata to CI/CD job token docs

Arpit Tripathirequested to merge
gitlab-community/gitlab-org/gitlab:525312-add-description-metadata-ci-job-token-docs into master

What does this MR do and why?

Add description metadata to CI/CD job token docs

Related to #525312

References

@lciutacu please review it

Edited by Arpit Tripathi

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