Update layout of merge conflict page

Proposal

Change the layout of the merge conflict page so that it looks like other pages in GitLab and the information hierarchy is improved

1. Move description of how to use this page to the top above the conflicts

Current	Proposal

Implementation plan

1. Make the changes to the file app/assets/javascripts/merge_conflicts/merge_conflict_resolver_app.vue
   • Move the "resolve-info" div as the first element in the div#conflicts
   • Remove the gl-mb-5 because that extra spacing is not needed
   • Update the text to be:
     • Resolve source branch {source-branch-name as link} conflicts using interactive mode to select Use ours or Use theirs, or manually using Edit inline.

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Note: The title was considered to be changed but it is a shared component across all merge request views so will revisit if necessary.