chore: Add enable token to authentication

[vasspilka]

When trying to follow the guide I encountered

Compiling 19 files (.ex)
** (EXIT from #PID<0.94.0>) an exception was raised:
    ** (Spark.Error.DslError) authentication -> tokens -> enabled?:
  The `password` password authentication strategy requires tokens be enabled because sign-in tokens are in use.

To fix this error you can either:

  1. disable sign in tokens by setting `sign_in_tokens? false` your password strategy, or
  2. enable tokens.

Adding this line fixed it

[vasspilka]

Already fixed in main