Offer slugs of merge request branch names

Original issue: #438861

Community contribution MR: !142371 (closed)

What does this MR do and why?

This is a Community contribution MR suggestion - !142371 (closed)

Introduce additional predefined variables containing slug versions of CI_MERGE_REQUEST_SOURCE_BRANCH and CI_MERGE_REQUEST_TARGET_BRANCH on merge request:

1. CI_MERGE_REQUEST_SOURCE_BRANCH_SLUG
2. CI_MERGE_REQUEST_TARGET_BRANCH_SLUG

Offer slugs of merge request branch names

We have $CI_COMMIT_REF_SLUG for $CI_COMMIT_REF_NAME, why not the same for $CI_MERGE_REQUEST_TARGET_BRANCH_NAME and $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME.

Closes #215273 (closed) and #438861.

Signed-off-by: Olliver Schinagl oliver@schinagl.nl

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