Enable ed25519 signature verification

warning: after this MR only commits signed with known key will be used for update, i.e. public key must be placed into well-known system places or added into remote config by using keys verification-key or verification-file.

• Add layer with ed25519 public key to be used for validation.
• Enable signature verification for OTA updates by adding sign-verify key for remote "origin"
• Use secret file with base64 encoded ed25519 signature during the build