text: Title: [Alerting] move always-available action variables to alerting/common
  Body: In PR https://github.com/elastic/kibana/pull/59756 action variables were added as a new property of alert types.  There are a handful of "always available" action variables such as `alertId` and `alertName`.  The definitions of these are duplicated in the `alerting` and `triggers_actions_ui` plugins:
  
  https://github.com/elastic/kibana/blob/ce1836b2af68a49b347f10e8cbdd92f9998ad616/x-pack/plugins/alerting/server/task_runner/transform_action_params.ts#L38-L47
  
  https://github.com/elastic/kibana/blob/ce1836b2af68a49b347f10e8cbdd92f9998ad616/x-pack/plugins/triggers_actions_ui/public/application/lib/action_variables.ts#L27-L42
  
  To prevent these from diverging in the future, we should move them to the alerting/common folder, and then reference them in the files above from there.