bypass helm repo add failure with option --force-update

Hi, in some cases which I don't clearly identify the root cause yet, the function add_helm_repositories returns either a warning or an error when repo already exists.

See two screenshots below.

$ add_helm_repositories
[INFO] --- add repository optical-tools-virt-helm-stable: https://xxxx.orange/artifactory/optical-tools-virt-helm-stable (with user/password auth)
"optical-tools-virt-helm-stable" already exists with the same configuration, skipping
Hang tight while we grab the latest from your chart repositories...
...Successfully got an update from the "optical-tools-virt-helm-stable" chart repository
Update Complete. ⎈Happy Helming!⎈

$ add_helm_repositories
[INFO] --- add repository optical-tools-virt-helm-stable: https://xxxx.orange/artifactory/optical-tools-virt-helm-stable (with user/password auth)
Error: repository name (optical-tools-virt-helm-stable) already exists, please specify a different name