Enhancement: Add chart to existing release

[tylerauerbeck]

As mentioned in: helm/chart-releaser-action#70, in different types of workflows it would be nice to be able to upload to an existing release instead of having to cut a seperate release just for/from CR. Is there any reason that this isn't / shouldn't be the case? Currently when trying to submit to an existing release, I am getting a 422 error.

Would be happy to submit a PR on this, just want to make sure this would be acceptable first.

[PhilippKuntschik]

I would love to see this feature.

This is relevant for repositories that do not only host the helm chart but for example other binary releases as well. You could of course have multiple releases for the same version, depending on the build pipeline, but IMO having one release with multiple download options would be more manageable.

[szaimen]

I would also really like to have this. It is even required in my case.

[ehakan]

Would love to see this.

We're using https://github.com/googleapis/release-please, which handles helm versions with release PRs, and also creates GitHub releases. Chart Releaser in this case creates duplicate releases.

[jasperkamerling]

We need this for the project I am working on because we want to publish the chart when we create a new release.
Therefor i created a pr #347