[influxdb2] Helm can not verify Helm Chart

Hello all,

I was trying to install the InfluxDB2 Helm Chart today and ran into a problem:

```shell
$ helm install influx influxdata/influxdb2 --verify --debug=true
install.go:173: [debug] Original chart version: ""
Error: failed to fetch provenance "https://github.com/influxdata/helm-charts/releases/download/influxdb2-1.0.16/influxdb2-1.0.16.tgz.prov"
helm.go:81: [debug] failed to fetch provenance "https://github.com/influxdata/helm-charts/releases/download/influxdb2-1.0.16/influxdb2-1.0.16.tgz.prov"
helm.sh/helm/v3/pkg/downloader.(*ChartDownloader).DownloadTo
/private/tmp/helm-20210204-50704-hycyjl/pkg/downloader/chart_downloader.go:120
helm.sh/helm/v3/pkg/action.(*ChartPathOptions).LocateChart
/private/tmp/helm-20210204-50704-hycyjl/pkg/action/install.go:675
main.runInstall
/private/tmp/helm-20210204-50704-hycyjl/cmd/helm/install.go:185
main.newInstallCmd.func2
/private/tmp/helm-20210204-50704-hycyjl/cmd/helm/install.go:120
github.com/spf13/cobra.(*Command).execute
/Users/brew/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/spf13/cobra@v1.1.1/command.go:850
github.com/spf13/cobra.(*Command).ExecuteC
/Users/brew/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/spf13/cobra@v1.1.1/command.go:958
github.com/spf13/cobra.(*Command).Execute
/Users/brew/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/spf13/cobra@v1.1.1/command.go:895
main.main
/private/tmp/helm-20210204-50704-hycyjl/cmd/helm/helm.go:80
runtime.main
/usr/local/Cellar/go/1.15.7_1/libexec/src/runtime/proc.go:204
runtime.goexit
/usr/local/Cellar/go/1.15.7_1/libexec/src/runtime/asm_amd64.s:1374
```

It seems that helm could not find the `.prov` files in the repository. If I remove the `--verify` argument from the command, it works.

I think providing the `.prov` files should be a good practice. If I understand it correctly the `.prov` file will be created by signing the packaged helm chart: https://helm.sh/docs/topics/provenance/

My System:
- Helm: `version.BuildInfo{Version:"v3.5.2", GitCommit:"167aac70832d3a384f65f9745335e9fb40169dc2", GitTreeState:"dirty", GoVersion:"go1.15.7"}`
- OS: macOS Mojave (10.14.6)

If you need some additional information, let me know.