Make AIOKafkaAdminClient an asynchronous context manager#1129

PeterJCLaw wants to merge 2 commits intoaio-libs:masteraio-libs/aiokafka:masterfrom

PeterJCLaw:admin-client-async-context-managerPeterJCLaw/aiokafka:admin-client-async-context-managerCopy head branch name to clipboard