Rewrite Mix Tasks with Igniter

[type1fool]

Overview

To generate and patch code more reliably, the existing Mix tasks should probably be rewritten to use Igniter.

Benefits

• Better/easier integration with Ash
  • See Add support for passkeys/webauthn team-alembic/ash_authentication#805
• Maybe less Regex for tasks that patch code
• Simpler dep installation & setup
  • mix igniter.install webauthn_components

TODO

• Update Mix.Tasks.Wac.Install
• Update README & installation docs