WL#17256: Export external databases from inside OCI

Migration Assistant will attempt to connect to the source instance from the jump host in OCI. If this connection is successful, the dump operation will be executed from the jump host instead of the host where Migration Assistant is running.

This improves execution time, as data is being dumped from a location closer to the destination Object Storage bucket.

1. Change the dependency of tasks, dump has to be executed later and it should depend on jumphost.
2. Extend remote_helper.py, add a method to lunch a dump operation.
3. Extend helper.py, add a method to execute a dump operation.
4. Add an interface to handle a dump operation, extract the code which executes dump locally from dbmigration_stages.py into a class which implements this interface, implement this interface for a remote dump.
5. It has to be possible to monitor the dump and interrupt it if needed.