Enhance usage ping with product adoption data

We made an EE usage ping in https://gitlab.com/gitlab-org/gitlab-ee/issues/380

https://gitlab.com/gitlab-org/gitlab-ee/uploads/b85639c029c2caa065aa27aa8220ffb3/image.png

If we add more data to this customer success can better help customers.

None of the data should be sensitive (project names, etc.) and everything should be transparent (visible in the JSON string show to the user).

I propose we send the total number of items for:

Comments
Groups
Users
Projects
Issues
Labels
CI Jobs or builds
Snippets
Milestones
Todos
Pushes
Merge requests
Environments
Triggers
Deploy keys
Pages
Project Services

We should ensure the above are all simple DB queries, if something is complex we shouldn't sent it.

Our version.gitlab.com should do the calculations, such as 'how many comments got made in the last 30 days', and 'did people suddenly stop using something'?

/cc @JobV @stanhu @ChadMalchow