#3652236 Gutenboarding: Add new tracking events

Changes proposed in this Pull Request

• Add tracking for vertical input when moving the focus out of the field or selecting a vertical.
  • selected_vertical_slug – The slug of the selected topic, defined only when the vertical is not free-form user input.
  • selected_vertical_label – Translated label of vertical or free-form user input.
• Add tracking for site title input when moving the focus out of the field.
  • has_selected_site_title – Whether site title has been entered on the acquire intent page.
• Add tracking for skipped vertical or site title inputs.
• Update calypso_newsite_step_leave event for IntentGathering step:
  • add selected_vertical_label prop which can be free-form user input.
  • change selected_vertical prop to selected_vertical_slug recording the same value as before
  • change selected_site_title prop to has_selected_site_title recording if a site title has been entered or not.
• Add tracking to PlansModal (open and closed with selected plan).
• Add tracking to signup controller to record the calypso_newsite_init before redirecting users to Gutenboarding.

Testing instructions

• The calypso_newsite_vertical_selected event should be fired when moving the focus off the vertical input that has a value (tabbing, clicking away, pressing enter or selecting a vertical) or when clearing the input.
• The calypso_newsite_site_title_selected event should be fired when moving the focus off the site title input (tabbing, clicking away).
• The calypso_newsite_vertical_skipped event should be fired when pressing grey I donʼt know link below it.
• The calypso_newsite_site_title_skipped event should be fired when pressing blue I donʼt know button or pressing Enter when focused on empty Site Title input to advance to Design Picker step.
• When advancing to Design Picker step, the calypso_newsite_step_leave event should should fire with props {flow: "gutenboarding", name: "IntentGathering", selected_vertical_slug: string | undefined, selected_vertical_label: string | undefined, has_selected_site_title: boolean}
• The calypso_newsite_modal_open event should fire with props {flow: "gutenboarding", name: "PlansGrid"} when clicking the Plans Button.
• The calypso_newsite_modal_close event should fire with props {flow: "gutenboarding", name: "PlansGrid", selected_plan: "free_plan"} when closing the Plans modal having the last selected plan slug instead of "free_plan".
• The calypso_newsite_init event should fire when A/B test condition is true, before redirecting user to /new.

Related to: #41059