At startup, check if there is a common protocol version between ORIGIN and TARGET

[joao-r-reis]

With #120 we're going to support Cassandra 2.0 but we also introduce a new scenario where a user might try to migrate from C* 2.0 to C* 4.0 and the proxy will start just fine but then client connections will fail because there's no common protocol version between both clusters.

We should add a check at startup so that zdm fails to start right away and the error message is clear.

┆Issue is synchronized with this Jira Task by Unito
┆Components: Proxy
┆Issue Number: ZDM-611