Configure Faker randomness with RSpec seed

There are at least two flakey specs:
* `spec/concepts/school_teacher/invite_spec.rb:14` [1]
* `spec/concepts/project/create_remix_spec.rb:125` [2]

I strongly suspect the extensive use of Faker in factories and spec
setup and the randomness associated with it may be the root cause of the
flakey specs. If nothing else it makes it hard to reproduce the spec
failures locally. Configuring Faker's randomness with the same seed
as RSpec is using and reporting should make it easier to reproduce any
flakey specs in the future.

[1]: https://github.com/RaspberryPiFoundation/editor-api/blob/f397e870f2a33cce1f53b9104c52314f5233572c/spec/concepts/school_teacher/invite_spec.rb#L14-L17
[2]: https://github.com/RaspberryPiFoundation/editor-api/blob/f397e870f2a33cce1f53b9104c52314f5233572c/spec/concepts/project/create_remix_spec.rb#L125-L128

Author: floehopper

spec/support/faker.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+RSpec.configure do |config|
+  config.before(:suite) do
+    puts "Faker randomized with seed #{config.seed}"
+    Faker::Config.random = Random.new(config.seed)
+  end
+end