Airshipctl Usability Improvement: default gpg key configuration & requirements for running commands

[eak13]

With the introduction of SOPS encryption, there is a need to generate a gpg key to handle encryption/decryption of secrets. This is currently not included in the default configuration and there is an expectation that users would perform this as a separate task. If a user has not read the documentation, they would be unfamiliar with this & will likely run into issues when attempting to configure & run commands.

First, look at updating airshipctl config init to include the option of generating a set of default gpg keys. This should not preclude users from providing their own keys.

Second, assess which commands truly need to have the gpg keys specified. For example, do commands like airshipctl phase list truly need them? Propose a path forward for which commands may be updated to not require.

This came from the 3/25 design call & will require further discussion