Support for Rails 7.0.x

[jrochkind]

We've been struggling with Rails autoloading for a while, around reference to Qa::LinkedData::AuthorityService in ./config/initializers/linked_data_authorities.rb

In Rails 6.1, it produced a deprecation warning as in #349, a PR that tried to resolve the deprecation warning. However that PR caused problems for downstream apps, and was reverted in #350.

Trying to test the app in Rails 7 -- it's moved on from deprecation warning to simply not working, with an error:

questioning_authority/config/initializers/linked_data_authorities.rb:1:in `<top (required)>': uninitialized constant Qa::LinkedData (NameError)
    from /Users/jrochkind/.gem/ruby/3.0.4/gems/railties-7.0.4/lib/rails/engine.rb:667:in `load'

I understand that in modern zeitwerk, you can't reference files that will be development load reloaded in an initializer (see deprecation warning in #349). But I'm a bit surprised and don't totally understand why it applies here, since files in an engine I thought weren't reloaded anyway.

Nonetheless, it looks like it works to move the file defining Qa::LinkedData::AuthorityService from ./app to ./lib, and add an explicit require of it at boot, in the engine.rb file. Tests now pass. I tried that because I knew ./lib wasn't involved in any kind of Rails autoloading, but can't say I 100% understand what's going on.

Con this change:

• It's a bit confusing to what files would be in ./lib vs ./app, it isn't totally consistent. But I left a comment trying to justify this one.
• If Qa::LinkedData::AuthorityService had referred to any files in ./app itself.. this might not work, as it still wouldn't be able to acccess them. But it didn't, so it was fine? Could become a problem in the future?
• I hate not totally understanding what's going on

Pro this change:

• Gets tests passing in Rails 7.0.x
• A very simple change
• I think it's very unlikely to break any apps

@cjcolvar since the last time I tried a fix you are the one who noticed it breaking an app... do you have any interest in testing this branch with whatever the last try broke, to ensure it's good this time before we merge?

Would close #351 I think

[jrochkind]

Note this PR includes adding 7.0.x to test matrix, and it passes!

[jrochkind]

Thanks @cjcolvar!

I'm going to do a tag and release too, unless someone tells me not to.