…ter system collections

This commit fixes two issues:

1. connection-options not being passed to MongoDBSourceBuilder:
   The internal Flink CDC key is \"connection.options\" (with dot), but users
   naturally pass \"connection-options\" (with hyphen). Added getConnectionOptions()
   to try both keys for compatibility. Also added .scheme() and .connectionOptions()
   calls to MongoDBSourceBuilder which were previously missing.

2. Unauthorized errors on system collections:
   MongoDB system collections (e.g. system.profile) cannot be accessed without
   elevated privileges. Added a filter to skip collections starting with \"system.\"
   during schema inference.