Provide a shipperctl command to refresh webhook secret

[parhamdoustdar]

Right now, there is no way of refreshing the secret for the webhook without downtime. This command would generate a new secret and replace it with the current secret. This allows operators to refresh a secret before it expires.

[parhamdoustdar]

Another way to do this could be to add a controller to Shipper that actively watches and refreshes the webhook secret before it expires. This is something for us to look into.