Update Rails version check if Rails 7 or newer is not being used.

[eclectic-coding]

@excid3 This removes Rails 6 installs #198 :

• Checked the method rails_7_or_newer? sooner so we can exit out before the install gets too far
• Included an error message and a note to delete the partial install directory

One edge case We are not checking if the user overrides the default system Rails version: rails _6.1.7_ new appname ....

[excid3]

We are not checking if the user overrides the default system Rails version What happens when they do that? Should still work right?

[eclectic-coding]

If their default system Rails version is 7, the check would assume it is a Rails 7 install.

If the user overrides, as mentioned above, and the default system Rails version is 7, it will fail as before.

If we would want to check for this edge case, we would need to figure out either how to read the version prefix in the cli args, or read from the already created Gemfile, which happens before the template.rb is accessed.

[eclectic-coding]

@excid3 I have addressed this edge case

Also, I removed the version check in the add_users method since we are now assuming Rails 7.