Adds `POST helm/api/prov` endpoint for helm repository allowing for upload of provenance files.
Tested manually to a degree but I really didn't want to mess with gpg
again so I'm not sure if helm will correctly verify the chart.
Initial draft made by gemini 3 flash but was finetuned somewhat.
Additionally there's an route that allows for upload of both files via
/api/charts - as separate files in form. If there's any interest in that
I guess it can be added but I think helm is moving to OCI anyway which
we support.
Fixes: https://github.com/go-gitea/gitea/issues/36678
Co-authored-by: silverwind <me@silverwind.io>
TheFox0x7
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