[Commands] Add spire:init and user:change-password commands

[Akkadius]

This PR adds the following commands

• spire:init [username] [password] --auth-enabled=true
• user:change-password [username] [password]

The initialization command is used to automate Spire installs which is what otherwise is done when a user first runs Spire from their server directory - asking them for a username, password and if they want to enable auth before setting up their instance of Spire.

The latter command is pretty straightforward, it is there to reset user passwords under a local context

go run main.go user:change-password akkadius password
INFO Password changed for user akkadius