fix(helm): maintain any existing comments in Chart.yaml

[ben-foxmoore]

As raised in #1944, the current approach for Helm charts (using js-yaml library) strips all comments from the file. This PR switches to using the popular yaml library (eemeli/yaml), and then patching the version value directly. This helps maintain any comments which have been added to the Chart.yaml - Renovate comments are the driving cause in our case.

Fixes #1944 🦕

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[ben-foxmoore]

CLA has just been signed.

[chingor13]

Thanks! Looks great!