--insecure-skip-tls-verify works only for K8s API connections

I am fetching a cert from the sealed secrets like this:

```
kubeseal --raw --insecure-skip-tls-verify=true --from-file=foo.secret --cert https://sealed-secrets.my-ingress.com/v1/cert.pem --namespace team-a --name team-a-foo
```

The ingresses certificate is self signed. I expected `--insecure-skip-tls-verify` to ignore tls verification, but looking at the code of sealed-secrets, this flag is never used inside this project and is probably only passed down to K8s Go client.

I believe it should be an easy fix though - should this flag be used for both use cases? If yes, I can try to submit a quick fix.

Start at the kubeseal command path for --raw and --insecure-skip-tls-verify, then trace how the --cert URL is fetched. Compare that path with the Kubernetes API connection path and verify the behavior using the self-signed sealed-secrets.my-ingress.com certificate described in the issue. Done means the flag's behavior is consistent for both connection types.

Written by the indexing model from the issue text.