* Fix issues with POSIX::Spawn, Terrapin and Ruby 3.0

Also improve the Terrapin monkey-patch for the stderr/stdout issue.

* Fix keyword argument handling throughout the codebase

* Monkey-patch Paperclip to fix keyword arguments handling in validators

* Change validation_extensions to please CodeClimate

* Bump microformats from 4.2.1 to 4.3.1

* Allow Ruby 3.0

* Add Ruby 3.0 test target to CircleCI

* Add test for admin dashboard warnings

* Fix admin dashboard warnings on Ruby 3.0

Fix #6856
Fix #6951

The cache store is explicitly used by some specs, but they were not
isolated and therefore not reliable. This fixes the issue by clearing
the cache after each specs.

* Correct site_contact_email typo

* Separate about more page into partials, add specs

* Add InstancePresenter to expose site details

* Clean up about controller, use instance presenter