Move some actions body to AsanaHelper + use ERB for processing templates

[ayoy]

Summary of changes:

• Simple Asana actions' implementation was moved to a dedicated AsanaHelper
  as functions: extract_asana_task_id, extract_asana_task_assignee,
  get_release_automation_subtask_id, get_asana_user_id_for_github_handle,
  upload_file_to_asana_task. Actions only call their respective helper method.
  This is to simplify using these functionalities from other actions (better not
  call action from action, but rather use helpers for common functionality).
• asana_add_comment, asana_log_message and asana_create_action_item actions
  now use ERB for processing templates. They take template_args Hash argument
  that provides template variables. For backward compatibility, environment variables
  are currently merged to template_args (with their keys lowercased), so that call
  sites in GHA workflows don't have to be updated. Future workflows implemented in
  fastlane will be able to use template_args with lowercased parameter names and
  eventually we'll remove the environment workaround.
• Unit tests were added for all templates, to verify that they're processed correctly.