Decouple helm invocations from local state

Currently, the behavior of deploying Helm charts is inconsistent across different roles. Some directly reference the upstream URL of the repository, some add the repository to the local Helm state first and then refer to that and some add it to the local state but never use it and refer to the upstream URL anyway.

Using the local Helm state has a few downsides:

• If the local Helm state is broken, the run will fail
• If a repository with the same name has already been configured locally, but with a different URL, this URL will be overwritten
• If update_repo_cache: true is forgotten, a stale version of the local copy of the repo will be used

This MR unifies the behavior and decouples all helm invocations completely from local state by referring directly to the upstream URL.

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Merge Prerequisites

• MR title (and description) are descriptive
• Code is readable and syntactically correct
• Code is understandable
• Documentation has been updated, if necessary
• Changelog has been updated, if necessary
• Commit messages look good

As a developer: please do not tick these boxes yourself. As a reviewer: please get yourself a hot cold beverage.