FIX: use allowlist and blocklist terminology (#10209)

This is a PR of the renaming whitelist to allowlist and blacklist to the blocklist.

spec/requests/users_controller_spec.rb

@@ -2982,9 +2982,9 @@ describe UsersController do
         expect(response.status).to eq(422)
       end
 
-      it "raises an error when the email is blacklisted" do
+      it "raises an error when the email is blocklisted" do
         post_user
-        SiteSetting.email_domains_blacklist = 'example.com'
+        SiteSetting.blocked_email_domains = 'example.com'
         put "/u/update-activation-email.json", params: { email: 'test@example.com' }
         expect(response.status).to eq(422)
       end