Add group wiki events to separate project and group wiki usage

What does this MR do and why?

Related to #301213 (closed).

This adds separate internal events tracking to group wikis.

We want to be able to distinguish group wiki traffic from project wikis. Normally we could do it by adding an additional property to existing create/update/delete_wiki_page events, but label and property for these are already taken and we wouldn't be able to use metric filters with custom properties.

Because of that, this MR adds new events for group wiki pages that are fired only when a wiki action on a group wiki happens.

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Before	After

How to set up and validate locally

1. Run bundle exec rails r scripts/internal_events/monitor.rb create_group_wiki_page
2. Do a wiki action on a group wiki and see the metrics increment.
3. Do a wiki action on a project wiki and see no change.
4. Repeat for update_group_wiki_page and delete_group_wiki_page.