Reintroduce the contribute/how/promote directory

After a limitation we hit when rewriting the Git history, we had to delete all files in the promote directory. We have to make sure we reintroduce the promote directory in the rewritten Git tails.git repo.

Parent Task: #6277 (closed)

Related issues

Blocks #8631 (closed)

Original created by @Dr_Whax on 8946 (Redmine)

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