- Use newer `ash_authentication` version since old version had
dependency resolution errors
- Add `ash-functions` to the extensions list
- Fixes compiler warning when the item is missing
* docs: improve security in the 'Get Started' guide
- Use a bang function to ensure that the `signing_secret` will raise an
exception if it is absent from the config (instead of just silently
evaluating to `nil`)
- Add config example for the secret signing token
- Add warning so that users are informed about the security implications
of using the basic configuration provided by the tutorial
- Rearrange the sections a bit so the `Token Generation` section comes
after the relevant code example
* docs: use correct function and modify secrets warning
