fix(vault): trim trailing newlines from kubeconfig before storing in vault add unwrapSOPSData function to handle SOPS data extraction

[OliverTrautvetter]

This pull request introduces several improvements and fixes related to handling kubeconfig storage, SOPS-encrypted vault data, and associated tests. The main changes ensure that kubeconfig files are stored without unwanted trailing newlines, add robust handling for SOPS-encrypted YAML files by unwrapping top-level data wrappers, and enhance testing to validate these behaviors.

Kubeconfig storage improvements:

• Trailing newlines are now trimmed from the kubeconfig content before storing it in the vault, preventing YAML formatting issues such as the use of |+ chomping.
• Tests were updated and extended to verify that trailing newlines are properly removed and to ensure the vault file does not contain unwanted YAML formatting.

SOPS/YAML handling improvements:

• Added the unwrapSOPSData function to automatically strip a top-level data block scalar wrapper from SOPS-encrypted YAML files, ensuring the vault parser receives the intended document structure.
• Integrated the unwrapping logic into the vault data parser and made the function available for testing.
• Added comprehensive unit tests for unwrapSOPSData to verify correct behavior with various YAML inputs, including normal, wrapped, and invalid documents.

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[joka134]

Looks good. One simple naming comment