Post sign-up: Add view events for all steps in the form

Created by: philipp-spiess

We currently don't have "view" events for all steps in the post sign-up panel.

• We have a generic PostSignUp event when the funnel starts (a proxy as to when the first step is shown).
• We have a specific event for UserSettingsRepositories.
• We can infer that the invite page is loaded by looking at UserInvitationsDiscoveredCollaborators.

However we don't know how many people load e.g. the teams beta panel.