Dry-run and validate synchronisation plan

[ramizpolic]

Goal

Currently, there is no way to tell if the given sync plan is valid or not. We would like to be able to notify user about plan validity.
This can be done through:

• Enabling dry-run option which will perform all the steps as usual, but skips sending the keys to destination secret store
• Providing a way to validate plan before execution (this should check if the query and transformation are valid for all keys) before performing any sync