LONDON (Reuters) – Britain’s finance and health ministers resigned on Tuesday, in what could be the final blow for Prime Minister Boris Johnson’s premiership. Johnson narrowly survived a confidence vote last month, giving him 12 months of immunity from another one. But some lawmakers in his Conservative Party have been trying to change the party rules to shorten that immunity period. Other lawmakers had appealed to Johnson’s top team of cabinet ministers to move against him. Below are options for how Johnson could be forced out, and how the process to find a replacement would work: \- Johnson …