Consider making clientId configurable

[mkobit]

Right now, it is hard coded to always be a unique UUID

cqlmigrate/src/main/java/uk/sky/cqlmigrate/LockConfig.java

Line 49 in df29e94

protected String clientId = UUID.randomUUID().toString();

It might be useful to derive that from a client's perspective, for example from a service that is running multiple pods in Kubernetes so the locks can be traced back.