Generate preview of SQL that will be executed by bundle

The EF Core bundle looks to be very helpful for simplifying automated deployment scenarios; however, it's still a bit of a black box as to what is going to happen when the bundle gets executed against a specific server. It would be very helpful to have the bundle generate the SQL script that is about to execute and return that, so that it can be reviewed e.g. by the DBA in a manual approval step in the build pipeline. Once approval is granted, then the bundle gets run for real.

I'm imagining something along the lines of `efbundle --dry-run this-needs-approval.sql`, which would check the migrations history of the destination database, and write out the to-be-executed migrations to the named file. This could then be picked up and published by the deployment pipeline (such as Azure DevOps or Octopus Deploy) and the build paused until the SQL script is reviewed; then `efbundle` can be executed without the `--dry-run` option, and the code will be executed.

[https://octopus.com/blog/dbup-database-deployment-automation](https://octopus.com/blog/dbup-database-deployment-automation) gives a nice example of how this can already be achieved using `DbUp` with a more full-featured report on what has changed, so not just the combined SQL script but scripts grouped by migration etc