Add ability to see project deployments at group-level (FE)

What does this MR do?

This adds the ability to see project-level deployments using a group-level cluster

Issue: https://gitlab.com/gitlab-org/gitlab-ee/issues/13392

CE Port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31575

Preview

Preview (empty state)

Testing the feature:

Note: This feature is behind a feature flag

1. Open a terminal in the project root
2. bundle exec rails console
3. Feature.enable(:view_group_cluster_deployments)
4. The feature is now enabled and should show up on the group cluster page once you've added a Group-level cluster.

The table can be populated with mockData in this MR (BE/FE integration will be done in a follow-up MR).

app/assets/javascripts/clusters/clusters_bundle.js

import mockData from '../../../../ee/spec/frontend/clusters/components/mock_data';

// line: 165
environments: mockData,

Does this MR meet the acceptance criteria?

Conformity

• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

TODO

• [ ] Should we partially enable the feature in CE? --> https://gitlab.com/gitlab-org/gitlab-ee/issues/13392#note_201853561
• Add/update tests.
• Add empty states --> https://gitlab.com/gitlab-org/gitlab-ee/issues/13392#note_201794784