Handles realtime with 2 states for environments table

What does this MR do?

• Merges the old state with the new to enable a better UX with realtime. No flickering is visible now.
• Moves the isLoading property to the store so we can show only one loader. Currently more than one would be visible.
• Keeps the same data structure because:

1. allows a much smaller code change
2. We would need to set some watchers to deal with updates in an object tree structure
3. Allows not to repeat the same logic across several components.

Why was this MR needed?

In order to fix deploy boards code - https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2311 https://gitlab.com/gitlab-org/gitlab-ee/issues/2677 - we first need to update the data in the ce repo

Does this MR meet the acceptance criteria?

• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/2677