git: http submodule relative url

Summary

• git: http submodule relative url

  man gitmodules

  submodule.<name>.url — Defines a URL from which the submodule repository can be cloned. This may be either an absolute URL ready to be passed to git-clone(1) or (if it begins with ./ or ../) a location relative to the superproject’s origin repository.

  submodule.<name>.branch — A remote branch name for tracking updates in the upstream submodule. If the option is not specified, it defaults to the remote HEAD.

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• Similar to !968 (merged)
• Follow-up for !1020 (merged)
• Cherry-pick to: none / 24.2 / 24.3
• Docs follow-up: not necessary / new issue