Adapt GlPagination to accept hasNextPage and hasPrevPage props from GraphQL response

See: gitlab-org/gitlab!44347 (comment 426133802)

if I recall correctly, GlPagination implementation dictates this extra code. A nice way to resolve this issue would be to adapt GlPagination to accept hasNextPage and hasPrevPage props from GraphQL response. Thus we won't need to do all that calculations here.

Lets do that