Enable connector log contexts in Connect Log4j configuration as per KIP-721

[james-johnston-thumbtack]

KIP-721 modified the default log4j log pattern to include connector context, like this:

connect.log.pattern=[%d] %p %X{connector.context}%m (%c:%L)%n

However, the default log4j configuration template used when CONNECT_LOG4J_APPENDER_STDOUT_LAYOUT_CONVERSIONPATTERN is not provided still uses the old log pattern: https://github.com/confluentinc/kafka-images/blob/v7.5.2/kafka-connect-base/include/etc/confluent/docker/log4j.properties.template#L6

I'd assume that all ConversionPattern values throughout this repository should also be similarly updated with a new default.