feat: make GIT_BRANCH and GIT_COMMIT_HASH available as env variables

[puehringer]

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Developer Checklist (Definition of Done)

Issue

• All acceptance criteria from the issue are met
• Tested in latest Chrome/Firefox

UI/UX/Vis

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Summary of changes

• Requires feat: make GIT_BRANCH and GIT_COMMIT_HASH available as build args github-workflows#219
• Makes GIT_BRANCH and GIT_COMMIT available if they are set in the environment

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Thanks for creating this pull request 🤗