Server name pattern is unnecessarily restrictive

As of DBZ-3427, Debezium doesn't allow using hyphens in the server name. The motivation is that the server name is used in JMX MBean names but according to the documentation, neither the mbean domain nor property values forbid using hyphens.

The problems are the following:

1. The server name in Debezium configuration may be derived from the actual server domain name which is allowed to contain hyphens, e.g. srv-01 (RFC-1035).
2. The server name from Debezium configuration is used to build the schema change topic name. Kafka topics in turn can be represented as Kubernetes resources by means of Strimzi. Kubernetes requires most of the resource names to be valid domain names which don't allow underscore.

Maintaining topic names containing underscores via Strimzi requires additional mapping of Kubernetes resource names to Kafka topic names which could be avoided if Debezium allowed using hyphens like it has been doing up until 1.6.0.Alpha1.