[translation] ./manage: add comments to new functions, rename job

./mange

  Comment functions:
  - babel.setup.translations.worktree
  - babel.weblate.to.translations
  - babel.translations.to.master
  - babel.master.to.translations
  BTW:
  - changed some cd into pushd
  - removed obsolete `set -x`
  - remove not needed echo from `last_commit_message=$(echo ..`

.github/workflows/translations-update.yml
docs/dev/translation.rst

  Rename job to: "create PR for additons from weblate"

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>