Add customer relations contacts viewer

What does this MR do and why?

We recently introduced the root component as a placeholder. This MR now wires it up to display a list of crm contacts.

Screenshots or screen recordings

How to set up and validate locally

1. Enable feature flag:
Feature.enable(:customer_relations)
2. Pick a group (I used flightjs) and create some contacts (either via graphiql or rails console):
mutation {
  customerRelationsContactCreate(input:
    {
      groupId: "gid://gitlab/Group/26"
      firstName: "Lee"
      lastName: "Tickett"
    }) {
    contact {
      id
      firstName
      lastName
    }
    errors
  }
}
3. Navigate to the contacts page: http://gdk.test:3000/groups/flightjs/-/crm/contacts (left hand nav menu from the group, "Customer relations -> Contacts")

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #2256