By Kate Abnett and Susanna Twidale BRUSSELS/LONDON (Reuters) – Proposals from southern European countries to intervene in energy markets have highlighted the difficulty facing an EU summit this week as it seeks to respond to record prices driven by Russia’s invasion of Ukraine. The 27 EU-member states are responsible for their own national energy policies. That complicates the European Commission’s task of devising a plan as it balances the goals of cutting reliance on Russian energy, limiting economic pain and not losing sight of its ambitions to cut carbon emissions. Following a first batch …