Add ability for JOGL moderators to get all users with certain skill(s)

Closes https://gitlab.com/JOGL/JOGL/-/issues/957

Reset the database and give the first user the moderator role.

> User.first.add_role(:moderator)

Add a few users, whose email is already confirmed and who will already come with a few skills:

> FactoryBot.create(:confirmed_user)
> FactoryBot.create(:confirmed_user)
> etc

POST /api/admin/users_with_skills {"skills": [1,2]}

You will get a response with users and a count. The count should match the number of users.