LONDON — Nigel Farage was hoping to sabotage Labour’s leadership fight. But a former ally is now trying to eat into his vote from the right — with some significant online help. Next month’s Makerfield by-election looked set to be a head-to-head battle between Farage’s Reform UK and Andy Burnham — a Labour mayor who hopes the contest will provide a stepping-stone in his push to become prime minister. But a Survation poll released this weekend put Restore Britain — a relatively obscure party led