add hook for clear pundit context

[furkanural]

Fix https://github.com/varvet/pundit/issues/811

As far as I can see, the caches are not being cleared after a UserContext change. Therefore, policies are being performed using the old UserContext. I would like to implement a simple solution to this issue. With this solution, caches can be cleared when deemed necessary.

class ApplicationController
  include Pundit::Authorization
  before_action :switch_account, if: :should_switch_account?

  def switch_account
    set_current_account(Account.find(params[:account_id]))
    clear_pundit_context!
  end

  def pundit_user
    UserContext.new(current_user, current_account)
  end
end

To do

• [x] I have read the contributing guidelines.
• [x] I have added relevant tests.
• [x] I have adjusted relevant documentation.
• [x] I have made sure the individual commits are meaningful.
• [x] I have added relevant lines to the CHANGELOG.

PS: Thank you for contributing to Pundit ❤️