Sensitive task data needs to be encrypted

[bohdan-shulha]

The public key, used for encryption, should be generated when the Swarm cluster is initialized on the agent's side. Private key will be kept on the Swarm Cluster and Public key will be transferred to ptah.sh. Then, the secret vars/secret files should be encrypted on the client side.

This way, we'd be able to store all the secure data on our database and don't worry about clean-ups or storing/transmitting unencoded critical access data.

Consider dropping the config creation for secrets at all: #110 (completed here ptah-sh/ptah-agent#51)

Scope:

• Secret Vars
• Secret Files
• S3 Storage passwords
• Docker Registry passwords
• Join Tokens (these have to be encoded by agent)