refactor: support rails authentication generator out of the box

[adrianthedev]

Note

This PR ended up just fixing a few unrelated bugs but produced the knowledge to build up [this guide](https://docs.avohq.io/3.0/guides/rails-authentication-scaffold.html that shows how to support Rails' authentication scaffold.

Description

Fixes #3361

Resources:

• https://superails.com/posts/178-new-rails-8-authentication-generator?playlist=rails-authentication-generator
• https://blog.corsego.com/rails-8-authentication
• https://www.bigbinary.com/blog/rails-8-introduces-a-basic-authentication-generator

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

Screenshots & recording

Manual review steps

1. Generate a new Rails 8 app
2. Run the authentication generator bin/rails generate authentication
3. check to see if Avo has the sign out button available

Manual reviewer: please leave a comment with output from the test if that's the case.

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This PR has been merged into main. The functionality will be available in the next release.

Please check the release guide for more information.