Add nonce for strict Content Security Policy

[frenkel]

Without a nonce an application with the following config will have errors in the browser.

Rails.application.configure do
  config.content_security_policy do |policy|
    policy.script_src :strict_dynamic
  end
end

Error (translated):

The page settings have blocked the execution of a script (script-src-elem) at http://localhost:3000/assets/hotwire_spark-d7e0ee73.js because it violates the following directive: ‘script-src 'strict-dynamic' 'nonce-e46d3874a949188ba1c4f5bbb3f93f8c'’