System notes when issue is transferred from one epic to another epic

• Define the system notes text for when an issue is transferred from one epic to another epic.
• This happens when a user adds an issue to one epic, but that issue already belongs to another epic.
• This is a follow up to https://gitlab.com/gitlab-org/gitlab-ee/issues/3947.
• Specify:
  • System note inside the issue that is transferred: Victor Wu @victorwu changed epic to &1234 6 days ago
  • System note inside the epic that lost the issue: Victor Wu @victorwu moved issue #1234 to epic &1234 6 days ago
  • System note inside the epic that gained the issue: Victor Wu @victorwu added issue #1234 from epic &1234 6 days ago

Icons are out of scope for this issue. They are covered in https://gitlab.com/gitlab-org/gitlab-ee/issues/4262