Add merged contribution event to Vue version of the 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 continues to build out the Activity section on the Overview tab.

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 adds the merged contribution event. In future MRs I will be iteratively adding support for the other contribution event types.

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

1. Disable the super sidebar if you have it enabled. The Vue profile does not yet support it. Will be supported in #389842
2. Open the rails console
   • bin/rails console
3. Enable the profile_tabs_vue feature flag
   • Feature.enable(:profile_tabs_vue)
4. Generate events by pasting the following into the Rails console and hitting enter

user = User.find_by_username('root')
merge_request = MergeRequest.merged.first
FactoryBot.create(:event, :merged, author: user, project: merge_request.project, target: merge_request)

5. Visit http://127.0.0.1:3000/root

MR acceptance checklist

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