Improve merge request approvals wording

Follow up to https://gitlab.com/gitlab-org/gitlab-ee/issues/5439

The wording of the approvals widget can be further improved make it clearer and the language more natural. There are also edge case that are still confusing.

Eligible approvers less than approvals required

When more approvers are required than assigned approvers. See https://gitlab.com/gitlab-org/gitlab-ee/issues/5439#note_90824808

Proposal

Update wording to be:

Requires 2 more approvals, 1 by [user]

Links / references