feature: delete package from registry

[volker-raschek]

Feature Description

We had on discord a small discussion about a missing feature, which results in this feature request:

I want to add a Gitea Action workflow to remove a helm package, when the git tag has been removed. The helm plugin cm-push does not support a delete option: chartmuseum/helm-push#147

Alternatively, I thought it would be possible with curl, but there is nothing documented.
https://docs.gitea.com/usage/packages/helm

The discord member 'TheFox' informed me, that the API does not provide a REST endpoint to delete a package from the registry. This leads than to this feature request.

Acceptance Criteria (AC):

1. Extend the REST API to delete the packages from the gitea registry. This feature request refers not only to Helm Charts but to all generally supported packages.
2. Adapt the documentation and describe how to delete via curl a package from the registry.

Screenshots

[TheFox0x7]

I'm basing my assumption of lack of any DELETE endpoint here

gitea/routers/api/packages/api.go

Lines 429 to 433 in 47d69b7

	r.Group("/helm", func() {
	r.Get("/index.yaml", helm.Index)
	r.Get("/{filename}", helm.DownloadPackageFile)
	r.Post("/api/charts", reqPackageAccess(perm.AccessModeWrite), helm.UploadPackage)
	}, reqPackageAccess(perm.AccessModeRead))

which I would expect if it was supported.