helm:add support for auto-generating gossip encryption secret

[kschoche]

Currently it is required to BYO the gossip encryption key, and this is documented in the values.yaml file:

 # gossipEncryption configures which Kubernetes secret to retrieve Consul's
 # gossip encryption key from (see https://www.consul.io/docs/agent/options.html#_encrypt).
 # If secretName or secretKey are not set, gossip encryption will not be enabled.
 # The secret must be in the same namespace that Consul is installed into.
 #
 # The secret can be created by running:
 #    kubectl create secret generic consul-gossip-encryption-key \
 #      --from-literal=key=$(consul keygen).
 #

It would be helpful to have the option to have helm auto-generate the gossip encryption key and install the secret at install time.

[yevgeniyo-ps]

@kschoche faced with the same and found this solution:
hashicorp/terraform-provider-consul#48