Setup activity section on Vue version of user profile

What does this MR do and why?

Related to #378677 (closed)

In &9056 we are migrating the user profile from HAML/jQuery to Vue. This is a large migration so we are splitting it up into many sections. This MR starts to build out the Activity section on the Overview tab.

Engineering note: There are many contribution events that we will need to support. These are documented in https://docs.gitlab.com/ee/user/profile/contributions_calendar.html#user-contribution-events. This MR sets up the scaffolding and creates the Vue component for one of the more simple events (approved). I decided to add the approved event in this MR to add more context into how each event type will be rendered. In future MRs I will be iteratively adding support for the other event types. All event components will extend ~/contribution_events/components/contribution_event/contribution_event_base.vue.

UX note: There is currently an incorrect bottom border in the tabs. This is due to a recent change in !118597 (merged). We will be removing the tabs and moving the navigation into the new sidebar in #389842. By removing the tabs we will be able to fix this bug and because this is behind a feature flag I am going to leave it as-is for now.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Open the rails console
   • bin/rails console
2. Enable the profile_tabs_vue feature flag
   • Feature.enable(:profile_tabs_vue)
3. Run the following commands to create an approved contribution event
   • user = User.find(1)
   • merge_request = MergeRequest.first
   • project = merge_request.project
   • FactoryBot.create(:event, :approved, author: user, project: project, target: merge_request)
4. Navigate to your profile

MR acceptance checklist

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