In RelationalBaseSourceConnector#validate (used as Connector#validate() for relational datastore connectors) we call RelationalBaseSourceConnector#validateConnection when only some connection related config options (like hostname etc) are valid. This can lead to exceptions.

For example when you provide a `schema.include.list` for a Postgres connector with an invalid regular expression like "+" as value but with working connection properties (which are checked in RelationalBaseSourceConnector#validate) the code assumes everything is fine to instantiate and validate the connection. But then, when instantiating an instance of the PostgresConnectorConfig the invalid regular expression gets compiled, leading to a PatternException.

This breaks the new PostgreSQL Connect REST Extension tests and it will also break Kafka Connect's validate connector-config endpoint (PUT /connector-plugins/($connector-plugin-name)/config/validate) which will also return the exception instead of the expected response with the config definition, errors, etc.

$ cat register-postgres-test.json 
{
        "connector.class": "io.debezium.connector.postgresql.PostgresConnector",
        "tasks.max": "1",
        "database.hostname": "postgres",
        "database.port": "5432",
        "database.user": "postgres",
        "database.password": "postgres",
        "database.dbname" : "postgres",
        "topic.prefix": "dbserver1",
        "schema.include.list": "+"
}

$ cat register-postgres-test.json | curl -X PUT -H "Content-Type: application/json" localhost:8083/connector-plugins/PostgresConnector/config/validate --data-binary @- | jq .
{
  "error_code": 500,
  "message": "java.util.regex.PatternSyntaxException: Dangling meta character '+' near index 0\n+\n^"
}